enlistment vs tour of duty

enlistment and tour of duty both are nouns.

Word	Noun	Adjective	Verb	Adverb
enlistment	Yes	No	No	No
tour of duty	Yes	No	No	No

As nouns, enlistment and tour of duty are synonyms defined as:

Other synonyms of enlistment include duty tour, hitch, term of enlistment, tour.

enlistment (noun)	tour of duty (noun)
the act of enlisting (as in a military service)	a period of time spent in military service
a period of time spent in military service