to depend on, to entrust with
乇 centers on placing reliance or responsibility on someone or something: depending on them or entrusting them with a task.
The historical origin of 乇 is uncertain. It appears as a component in other characters, but its independent development is not clearly established.
The top stroke 丿 looks like a person leaning down, and the bottom 七 resembles a bent support. Picture someone leaning on a crooked staff, depending on it for balance.
For タク, imagine entrusting a tack to someone: you hand them a thumbtack and say 'tack' (タク) as you depend on them to keep it safe.