noun
leaving everything up to someone else; entrusting completely
Describes a situation where one person delegates all responsibility to another and does not get involved afterward. Often used with verbs like する or になる.
彼に任せきりにして、私は何も手伝わなかった。
I left everything up to him and didn't help at all.
このプロジェクトは彼女に任せきりだ。
This project has been completely entrusted to her.
任せる is the base verb meaning 'to entrust'; 任せきり emphasizes that after entrusting, one does not intervene or check.
丸投げ is a more casual or business term for outsourcing or dumping a whole task on someone, often with a negative nuance of abdication.
Compound of the continuative form of 任せる (to entrust) and the suffix きり (only, just), indicating that after entrusting, nothing further is done.