detachment vs rearguard

detachment and rearguard both are nouns.

Word	Noun	Adjective	Verb	Adverb
detachment	Yes	No	No	No
rearguard	Yes	No	No	No

As nouns, rearguard is a hyponym of detachment; that is, rearguard is a word with a more specific, narrower meaning than detachment:

detachment: a small unit of troops of special composition
rearguard: a detachment assigned to protect the rear of a (retreating) military body

Other hyponyms of detachment include bodyguard, patrol, picket, press gang, provost guard.

detachment (noun)	rearguard (noun)
the act of releasing from an attachment or connection	a detachment assigned to protect the rear of a (retreating) military body
coming apart
avoiding emotional involvement
a small unit of troops of special composition
the state of being isolated or detached