Green’s Dictionary of Slang

a euph. for fuck all n., i.e. absolutely nothing.

1919		W.H. Downing Digger Dialects 22: f.a. [...] ‘Fanny Adams’ or ‘Sweet Fanny Adams’ — nothing; vacuity.
1924		(con. WWI) A.G. Pretty Gloss. of Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: f.a. [...] Fuck All; Fanny Adams; Nothing; vacuity.
1927		(con. WW1) P. MacDonald Patrol 129: ‘Nothing over there?’ [...] ‘Fanny Adams! ’cept sand’.
1938		G. Kersh Night and the City 163: So I starts playing about; [...] tickling him, and all that Fanny Adams.
1946		R. Rivett Behind Bamboo 396: F.A. (sweet), nothing at all [...] Fanny Adams, nothing at all.
1951		D. Stivens Jimmy Brockett 219: What he knew about education was F.A.
1970		G.F. Newman Sir, You Bastard 92: There’s FA wrong with my morals.
1989		J. Morton Lowspeak.