|Origin:||will I nill I '(whether) I am willing (or) I am unwilling'; nill 'to be unwilling' (11-19 centuries), from Old English nyllan, from ne 'not' + wyllan ( WILL1)|
if something happens willy-nilly, it happens whether you want it to or not:
He found himself drawn, willy-nilly, into the argument.
without planning, organization, or control:
Companies were accused of raising prices willy-nilly.