detainment vs confinement

detainment and confinement both are nouns.

Word	Noun	Adjective	Verb	Adverb
detainment	Yes	No	No	No
confinement	Yes	No	No	No

As nouns, confinement is a hypernym of detainment; that is, confinement is a word with a broader meaning than detainment:

detainment (noun)	confinement (noun)
a state of being confined (usually for a short time)	the act of restraining of a person's liberty by confining them
	the act of keeping something within specified bounds (by force if necessary)
	the state of being confined
	concluding state of pregnancy; from the onset of contractions to the birth of a child