用法:
1 each of a series of teeth on the edge of a wheel, that fit between those of a similar wheel, so that each wheel can cause the other one to move （齿轮的）轮牙; 轮齿. =>illus 见插图.

用法:
2 (idm 习语) a cog in the ma`chine (infml) person who plays a necessary but small part in a large organization or process 不重要的但不可少的人.

• keep one's shirt on(put one's shirt on)
• keep open house(keep the house open)
• keep silence(keep silent)
• keep the ball rolling(set the ball rolling)
• keep watch for(keep watch on)
• kick one's heels(kick up one's heels)
• kind(kindly)
• kind(sort)
• knit(knitted)
• know better(know any better)
• know(learn)
• know(recognize)
• know(think)
• labouring people(working people)
• lack(fall short of)
• laden(loaded)
• large(largely)
• last month(the last month, the past month)
• last(lastly)
• last(latest)
• last(latter)
• last(past)
• last(the last)
• late(lately)
• late(later on)