"to vacillate," 1782, from adverbial expression to stand shilly-shally (1703), earlier shill I, shall I (1700), a fanciful reduplication of shall I? (cf. wishy-washy, dilly-dally, etc.). From 1734 as an adjective, by 1755 as a noun. Related: Shilly-shallying (1816).
To vacillate; be irresolute: For god sake, stop shilly-shallying and make up your mind
[1782+; found by 1700 in form shill I shall I]