adverb
unusually; uncharacteristically
Describes a situation or behavior that is different from the usual state. Often used when someone acts out of character or something feels different from normal.
今日はいつになく早く起きた。
Today I woke up unusually early.
彼はいつになく静かだった。
He was uncharacteristically quiet.
A more literal phrase meaning 'differently from usual'. いつになく is a fixed adverbial expression that is more concise and idiomatic.
Derived from いつ (when) + に + なく (adverbial negative of ある), literally 'not being at any time', which evolved to mean 'unusually' or 'unlike usual'.