Do (double) duty as American verb phrase
Used to describe a person who does more than one task, duty, role or job simultaneously
She is making use of her own abilities to make a living, so she is doing double duty as a full-time banker and a part-time tutor.
Used to describe something that is capable of serving two functions
I really like this piece of furniture as it does double duty as a desk and a bookshelf.
To become someone's work.
The verb "do" should be conjugated according to its tense.
To not have any children
He is an old man having neither chick nor child, so when he gets sick no one pays him a visit.