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