Green’s Dictionary of Slang

(orig. US) to inform, to explain.

1945		E. Newhouse Many are Called (1951) 192: [...] Can you fill me in on them?
1958		R. Chandler Playback 185: Like to fill us in a litttle, Mr. Kinsolving?
1970		T. Parker Frying-Pan 152: What I meant by ‘filling you in’ was I thought you might like to know how it looked to a regular convict.
1971		R.D. Pharr S.R.O. (1998) 263: ‘And lie? You should have heard me and that old man fill in my investigator’.
1982		G.V. Higgins Patriot Game (1985) 107: When I have scouted around Fahey a little, I will fill you in. But I will not tell you everything.
1992		K. Lette Llama Parlour 178: Have I filled ya in on how much cashola I’m gonna make?
2001		N. Griffiths Sheepshagger 2: Well, enlighten us then, Danny [...] go on, fill us in, cos I’m dying to fuckin know, we all are.
2013		T. Robinson Hard Bounce [ebook] ‘Now that we’re all introduced, why don’t one of you fill me in on what the fuck this is all about’.
2020		G. Disher Consolation 87: ‘Maggie, can you fill these gentlemen in? They want to know about Leon Ayliffe’.