detainment vs detention

detainment and detention both are nouns.

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

As nouns, detainment and detention are synonyms defined as:

detainment and detention: a state of being confined (usually for a short time)

Other synonyms of detainment include custody, hold.

detainment (noun)	detention (noun)
a state of being confined (usually for a short time)	a punishment in which a student must stay at school after others have gone home
	a state of being confined (usually for a short time)