Green’s Dictionary of Slang

decent adv.

acceptably.

1829		Belfast News-Letter 2 Jan. 4/1: You thought that I was buried deep, / Quite decent like.
1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor II 249/2: They guv me 2s. 6d., and a tidy shirt, and a pair of blucherers, and mended up my togs for me decent.
1880		Henley & Stevenson Deacon Brodie I tab. I iv: It’s the least we can do to behave dacent.