custody vs safekeeping

custody and safekeeping both are nouns.

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

As nouns, safekeeping is a hypernym of custody; that is, safekeeping 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
safekeeping: the responsibility of a guardian or keeper

Other hypernyms of custody include guardianship, keeping.

custody (noun)	safekeeping (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
a state of being confined (usually for a short time)