Green’s Dictionary of Slang

ace adj.

[ace n. (3)]
[1930s+] (orig. US)

1. (also acey, acey-deucey) best, excellent, wonderful.

2. expert.

In compounds

ace boon coon (n.)

see separate entry.

ace boy (n.) (also ace buddy, ace-cut) [SE boy/buddy n. (2)/? SE cut]

[1950s+] (US campus) one’s best friend.

ace-flat (adj.) [SE flat, absolute, downright, unqualified]

[1940s] (US) excellent, first-rate.

ace-lover (n.)

[1940s] (US black, mainly Southern/Midwest) one’s most important lover, the most important member of the opposite sex one knows, e.g. a husband, a pimp, a boyfriend.

aceman (n.)

[1950s] (US teen) the leader of a teen street gang.

ace queen (n.)

[1970s+] (N.Z./US gay/prison) a very effeminate (prison) homosexual.