cog

1. N-COUNT A cog is a wheel with square or triangular teeth around the edge, which is used in a machine to turn another wheel or part. 齒輪

2. PHRASE If you describe someone as a cog in a machine or wheel, you mean that they are a small part of a large organization or group. (大型機搆或組織中的)小人物[v-link PHR]

Mr. Lake was an important cog in the republican campaign machine. 雷尅先生是共和黨競選機器中一個小人物，但卻發揮了重要作用。

3. N-COUNT a tenon that projects from the end of a timber beam for fitting into a mortise (木工)凸榫