Green’s Dictionary of Slang

fill in (on) v.

[i.e. to fill in blank spaces]

(orig. US) to inform, to explain.

[US]E. Newhouse Many are Called (1951) 192: [...] Can you fill me in on them?
[US]R. Chandler Playback 185: Like to fill us in a litttle, Mr. Kinsolving?
[UK]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.
[US]R.D. Pharr S.R.O. (1998) 263: ‘And lie? You should have heard me and that old man fill in my investigator’.
[US]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.
[UK]K. Lette Llama Parlour 178: Have I filled ya in on how much cashola I’m gonna make?
[UK]N. Griffiths Sheepshagger 2: Well, enlighten us then, Danny [...] go on, fill us in, cos I’m dying to fuckin know, we all are.
[US]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’.
[Aus]G. Disher Consolation 87: ‘Maggie, can you fill these gentlemen in? They want to know about Leon Ayliffe’.
[US]C. Stella Joey Piss Pot 83: ‘I’m doing my best here, Mary. I’m trying to fill you in’.