Green’s Dictionary of Slang

trim v.

[SE trim, to cut the hair, thus to ‘fleece’]

1. [early 16C+] (also trim up) to beat, to trounce, to defeat.

2. (also trim up) in fig. (non-physical) senses; to defeat in competition.

3. [early 16C+] to reprimand, to scold.

4. [17C–18C; 1960s+] to have sexual intercourse; thus trimming n.

5. [late 17C+] to cheat of money or possessions; thus trimming n. and adj.

6. to explain.

In phrases

trim someone’s buff (v.) [SE trim, to clip + buff, bare skin]

[late 18C] to deflower a woman.

trim someone’s jacket (v.) (also swinge someone’s jacket) [cf. SE dress, array, to beat/swinge, to thrash]

[mid-18C–early 19C] to beat, to thrash someone.

trim someone’s rim (v.) [assonance]

[1970s] (US) to have anal intercourse.

trim up (v.)

1. see sense 1 above.

2. see sense 2 above.