Green’s Dictionary of Slang

royal n.1

[? fig. use of Sp. real, a coin of very low value and considered inferior to UK sterling; such individuals have low social status; the US use is prob. ignorant of such overtones]

1. (W.I., Jam.) any black person from a race other than West Indian; thus in combs. coolie royal (East Indian) and joc./derog. jackass-royal, monkey-royal.

2. (W.I., also Chiney-Royal) a mixed black/Chinese person.

3. (US black) a West Indian.

4. (W.I., Trin.) the buttocks [fig. use of sense 1; in this case the physical ‘lowness’ of the buttocks].

In phrases

catch one’s royal (v.)

[1950s] (W.I.) to have no money.

in one’s royal (adj.) [? Carib.E royal/rial, arrogant, high and mighty]

[20C+] (W.I.) very drunk.