custody vs keeping

custody and keeping both are nouns.

Word	Noun	Adjective	Verb	Adverb
custody	Yes	No	No	No
keeping	Yes	No	No	No

As nouns, keeping is a hypernym of custody; that is, keeping is a word with a broader meaning than custody:

custody: (with `in') guardianship over; in divorce cases it is the right to house and care for and discipline a child
keeping: the responsibility of a guardian or keeper

Other hypernyms of custody include guardianship, safekeeping.

custody (noun)	keeping (noun)
holding by the police	the responsibility of a guardian or keeper
(with `in') guardianship over; in divorce cases it is the right to house and care for and discipline a child	conformity or harmony
a state of being confined (usually for a short time)	the act of retaining something