Green’s Dictionary of Slang

(orig. Anglo-Ind.) a letter, a note, any small piece of paper inscribed with writing, usu. instructions.

1698		J. Fryer Account of East India and Persia III iv 126: I sent my Gulleon Peon…with his Master’s Chitty, or Pass, to the governor.
1786		Tippoo’s Letter 284: Every merchant from Muscat who brings you a chitty from Meer Kâzim [Y&B].
1829		Memoirs of Colonel Mountain (2nd edn) 80: He wanted a chithee or note, for this is the most note-writing country under heaven [Y&B].
1886		Yule & Burnell Hobson-Jobson (1996) 203: chit, chitty, s. A letter or note, also a certificate given to a servant or the like; a pass.
1891		Civil & Milit. Gaz. (Lahore) 21 May 2/1: ‘In your honour’s hand was a piece of paper, blue paper. [...] You put this chitti in your honour’s mouth — and as I looked [...] your honour chewed the paper and then your honour swallowed it’.
1941		‘Rows and Rows and Rows’ in C.H. Ward-Jackson Airman’s Song Book (1945) 140: With little chitties that we forged we took them by surprise.
1966		(con. 1954) J. McGrath Events While Guarding the Bofors Gun I i: I know a bloke who saved up chitties for seven thousand cheap fags.