i-adjective
unusual; uncharacteristic; unlike one's usual self
Describes a situation, behavior, or state that is different from what is normal or expected for a person or thing. Often used when someone acts out of character.
今日の彼はいつにないほど静かだ。
He is unusually quiet today.
いつにない寒さで、桜の開花が遅れている。
The unseasonable cold has delayed the cherry blossoms.
Derived from いつ (when) + に + ない (not), literally 'not at any time', but used idiomatically to mean 'unusual' or 'uncharacteristic'.