Definition of "Tillie"

Without reason, against prudence, and at a moment’s notice, he fell in love with a frivolous, golden-haired girl who used to tear about Simla Mall on a high, rough waler, with a blue velvet jockey-cap crammed over her eyes. Her name was Venner—Tillie Venner—and she was delightful.

1887, Rudyard Kipling, Wressley of the Foreign Office