The Chinese word for thumb is
拇指

mǔ zhǐ

Chinese Definition

thumb
1. 拇指
Components
拇
1. (anatomy) thumb
2. (anatomy) big toe
指
1. finger
手指 - finger
2. to point; to point out; to aim
指出 - to point out
指人 - to point at a person
3. to indicate; to show; to demonstrate
4. to refer to; to mean
春天指的是冬天後面的那個季節。 - Spring refers to the season after winter.
5. to rely on; to depend on
6. to criticize; to rebuke
7. to make one’s hair stand on end