arm

arm (someone, something, or oneself) with (something)

1. To provide or equip someone, something, or oneself with weapons of some kind. Often used in passive constructions. They are arming the local militia with machine guns and grenades. The peasants were armed with pitchforks and scythes as they stormed the military garrison. It's a pretty cool robot, but why on earth did you arm it with a pair of flamethrowers?
2. To provide someone, something, or oneself with some necessary means of achieving victory. Often used in passive constructions. I try to arm my students with knowledge about how the world really works. We went into the trial armed with surveillance footage that proved the company's involvement in the incident.
See also: arm
Farlex Dictionary of Idioms.

arm (someone against someone or something) (with something)

to equip someone with whatever is needed to fight against someone or something. They armed themselves against the enemy with guns and ammunition. The government armed the soldiers with the new guns.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

arm

n. a police officer. (see also long arm of the law.) What’ll you do if the arms come in while you’re sawing the bars of your cell?
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See:
  • (as) busy as a one-armed paperhanger (with an itch)
  • a babe in arms
  • a bang in the arm
  • a call to arms
  • a list as long as your arm
  • a shot in the arm
  • an arm and a leg
  • arm
  • arm (someone, something, or oneself) with (something)
  • arm and a leg
  • arm candy
  • arm in arm
  • arm to the teeth
  • arm up
  • armed and dangerous
  • armed at all points
  • armed to the teeth
  • arm's length
  • arm-twister
  • arm-twisting
  • as long as (one's) arm
  • as long as your arm
  • at arm's length
  • babe in arms
  • bang in the arm
  • be armed to the teeth
  • bear arms
  • break (one's) arm patting (oneself) on the back
  • busy as a beaver
  • chance (one's) arm
  • chance your arm
  • cost a pretty penny
  • cost an arm and a leg
  • cost an arm and a leg/a pretty penny, to
  • cost/pay an arm and a leg
  • could (do something) with one arm tied behind (one's) back
  • fling (one's) arms up
  • fling (one's) arms up in (some emotion)
  • fling up (one's) arms
  • fling up (one's) arms in (some emotion)
  • fold (someone) in (one's) arms
  • fold somebody in your arms
  • get (one's) arms around (something)
  • give (one's) right arm
  • give an arm and a leg (for something)
  • give an arm and a leg for
  • give an arm and a leg for something
  • give one's eyeteeth
  • give one's right arm, to
  • give right arm
  • give your right arm
  • governments have long arms
  • greet (someone or something) with open arms
  • have a good arm
  • have calluses from patting own back
  • hold (one) at arm's length
  • in arms
  • in the arms of Morpheus
  • keep (one) at arm's length
  • keep (someone or something) at arm's length
  • keep at arm's length from
  • keep at arm's length from (someone or something)
  • keep at arm's length, to
  • keep somebody at arm's length
  • keep someone at arm's length
  • keep someone or something at arm's length
  • Kings have long arms
  • lay down (one's) arms
  • lay down arms
  • lay down your arms
  • list as long as (one's) arm
  • long arm
  • long arm of the law
  • long arm of the law, the
  • long as your arm
  • make a long arm for (something)
  • one-arm bandit
  • one-armed bandit
  • open arms, with
  • passage of arms
  • pay an arm and a leg
  • pay an arm and a leg (for something)
  • put the arm on
  • put the arm on (one)
  • put the arm on someone
  • put the arm/bite on somebody
  • put the bite on (one)
  • put the squeeze on (one)
  • receive (someone or something) with open arms
  • receive with open arms
  • short arms inspection
  • shot in the arm
  • shot in the arm, a
  • small arms
  • stretch your arm no further than your sleeve (will reach)
  • stretch your arm no further than your sleeve will reach
  • strong-arm
  • strong-arm man
  • strong-arm tactics
  • take up arms
  • take up arms (against someone or something)
  • talk (one's) arm(s) off
  • talk someone's arm off
  • the long arm of coincidence
  • the long arm of the law
  • throw (one's) arms up in despair
  • throw (one's) arms up in frustration
  • throw (one's) arms up in horror
  • throw up (one's) hands
  • throw up (one's) hands in despair
  • throw up your hands/arms in despair, horror, etc.
  • twist (one's) arm
  • twist arm
  • twist somebody's arm
  • twist someone’s arm
  • twist someone's arm
  • up in arms
  • up in arms about
  • up in arms about (something)
  • welcome (someone or something) with open arms
  • welcome someone with open arms
  • welcome something with open arms
  • with an arm tied behind (one's) back
  • with one arm tied behind (one's) back
  • with one arm tied behind one's back
  • with open arms
  • within arm's reach
  • would give your right arm for
  • would give your right arm for something/to do something
References in classic literature
Once I was arrested by the distant voice of Montgomery bawling, "Coo-ee--Moreau!" My arm became less painful, but very hot.
"Go back in," he said, taking my arm. "They're mad.
Island of Doctor Moreau
"Do you hear, Rosa?" said Gryphus, "the prisoner is going to set my arm, that's a saving; come, assist me to get up, I feel as heavy as lead."
Rosa lent the sufferer her shoulder; he put his unhurt arm around her neck, and making an effort, got on his legs, whilst Cornelius, to save him a walk, pushed a chair towards him.
The Black Tulip
Genevieve saw her lover's arms drop to his sides as his body lifted, went backward, and fell limply to the floor.
He knew only the blind desire to destroy, shook Joe in the clinches as a terrier might a rat, strained and struggled for freedom of body and arms, and all the while Joe calmly clutched and held on.
The Game
After them came twenty-seven sumpter horses carrying tent-poles, cloth, spare arms, spurs, wedges, cooking kettles, horse-shoes, bags of nails and the hundred other things which experience had shown to be needful in a harried and hostile country.
He bore no arms save the long and heavy sword which hung at his saddle-bow; but Terlake carried in front of him the high wivern-crested bassinet, Ford the heavy ash spear with swallow-tail pennon, while Alleyne was entrusted with the emblazoned shield.
The White Company
Suddenly I came to myself and, with that strange instinct which seems ever to prompt me to my duty, I seized the cudgel, which had fallen to the floor at the commencement of the battle, and swinging it with all the power of my earthly arms I crashed it full upon the head of the ape, crushing his skull as though it had been an eggshell.
It is true I held the cudgel, but what could I do with it against his four great arms? Even should I break one of them with my first blow, for I figured that he would attempt to ward off the cudgel, he could reach out and annihilate me with the others before I could recover for a second attack.
Princess of Mars
He had seen, on the streets, with persons of her class, that the women took the men's arms. But then, again, he had seen them when they didn't; and he wondered if it was only in the evening that arms were taken, or only between husbands and wives and relatives.
Martin Eden
His puissance, trusting in th' Almightie's aide, I mean to try, whose Reason I have tri'd Unsound and false; nor is it aught but just, That he who in debate of Truth hath won, Should win in Arms, in both disputes alike Victor; though brutish that contest and foule, When Reason hath to deal with force, yet so Most reason is that Reason overcome.
Paradise Lost
And if it be urged that whoever is armed will act in the same way, whether mercenary or not, I reply that when arms have to be resorted to, either by a prince or a republic, then the prince ought to go in person and perform the duty of a captain; the republic has to send its citizens, and when one is sent who does not turn out satisfactorily, it ought to recall him, and when one is worthy, to hold him by the laws so that he does not leave the command.
Prince
In some governments the power is vested not only in those who bear arms, but also in those who have borne them.
A Treatise on Government
The gentleman grasped her firmly by the shoulders, and being so fully occupied with holding her back, he was unable to put a hand to his veil which was falling off, as it did at length entirely, and Dorothea, who was holding the lady in her arms, raising her eyes saw that he who likewise held her was her husband, Don Fernando.
Don Quixote