one part of a large system or organization.

He was just a small cog in the large wheel of organised crime.

This warehouse is an important cog in our distribution machine.

• a miracle-worker
• a misery guts
• a miss is as good as a mile.
• a mixed bag
• a Monday morning quarterback
• a money-spinner
• a monkey on back
• a monkey on someone's back
• a monkey on your back
• a mother lode of
• a mother lode of something
• a mother's boy
• a mountain to climb
• amount to
• amount to a hill of beans
• amount to something
• amount to the same thing
• amour propre
• a mouth to feed
• a movable feast
• a mug's game
• a mummy's boy
• a mutual admiration society
• a mystery to
• a mystery to you