fort vs close in

fort is a noun but close in is not a noun.

Word	Noun	Adjective	Verb	Adverb
fort	Yes	No	Yes	No
close in	No	No	Yes	No

As verbs, close in is a hypernym of fort; that is, close in is a word with a broader meaning than fort:

Other hypernyms of fort include enclose, inclose, shut in.

fort (noun)	close in (noun)
a fortified defensive structure
a fortified military post where troops are stationed

fort (verb)	close in (verb)
station (troops) in a fort	surround completely
enclose by or as if by a fortification	advance or converge on
gather in, or as if in, a fort, as for protection or defense