head over heels in love; madly in love; crazy about
Colloquial expression meaning to be completely infatuated or deeply in love with someone. Often used in the pattern 〜に首ったけ.
He's head over heels in love with his new girlfriend.
Those two seem to be crazy about each other.
Most common spelling; uses 首 (neck) with the colloquial geminate ったけ.
Rare variant using 丈; may be encountered in older or stylistic writing.
Rare variant using 頸; 頸 is a less common kanji for 'neck'.
From 首丈, literally “up to the neck,” with 丈 expressing extent. The image of being immersed up to the neck produced the sense “completely infatuated.”