chink

A minor but very detrimental flaw or weakness. Yeah, he's brilliant, but his violent temper has destroyed many business relationships—it's a real chink in his armor. The criminal's tendency to use his own cell phone to conduct business was the chink in the armor the police needed to put him in jail.

To fill in or patch narrow openings, such as cracks or fissures (chinks), of something. A noun or pronoun can be used between "chink" and "up." We live in an area that experiences a lot of earthquakes each year, so we've gotten pretty good at chinking up the walls of our house.

Fig. a special weakness that provides a means for attacking or impressing someone otherwise invulnerable. (Alludes to an opening in a suit of armor that allows a weapon to penetrate.) Jane's insecurity is the chink in her armor. The boss seems mean, but the chink in his armor is that he is easily flattered.

A vulnerable area, as in Putting things off to the last minute is the chink in Pat's armor and is bound to get her in trouble one day . This term relies on chink in the sense of "a crack or gap," a meaning dating from about 1400 and used figuratively since the mid-1600s.

If someone or something has a chink in their armour, they have a weakness that people can take advantage of, although they seem very strong and successful. Note: `Armour' is spelled `armor' in American English. With their superior knowledge, they might find the chinks in his armour. Labour leaders hope to use their annual conference to attack what they currently see as the most vulnerable chink in the government's armour. Note: A chink is a small hole or opening.

A vulnerable spot, a weakness. The term alludes to the medieval knight’s armor made of mail—interlinked rings of metal jointed at various points. When a crack, or chink, developed between the links or joints, he was less protected against a spear or arrow. The noun “chink” has been used figuratively for such a fissure since the 1600s, and the current term came soon afterward. See also Achilles' heel.