leaving everything up to someone else; entrusting completely
Often implies a hands-off approach where one person delegates entirely to another, sometimes with a nuance of neglect or over-reliance.
I've left everything up to him and haven't done anything myself.
It's not good to leave all the work to your subordinates.
Alternate kanji form using 切.
From the verb 任せる (to entrust) + っきり (emphatic suffix indicating 'only' or 'completely').