/ ˌwɪli ˈnɪli; NAmE / adverb ( informal )
1.
whether you want to or not :
She was forced willy-nilly to accept the company's proposals.
2.
in a careless way without planning :
Don't use your credit card willy-nilly.
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WORD ORIGIN
early 17th cent.: later spelling of will I, nill I I am willing, I am unwilling .