Green’s Dictionary of Slang

(orig. gay) wonderful.

2002		Indep. 12 Nov. 18: That was fabuloso, letting down their car tyres before they could get there.
2003		(ref. to 1960s) Baker & Stanley Hello Sailor! 99: Shipmates might talk to each other in Polari about who was fanciable: their dolly eek (pretty face), bona riah (nice hair), fabulosa ogles (fantastic eyes) and shapely lallies (legs).
2019		P. Baker Fabulosa 292/1: fabulosaa wonderful.