gather vs fort up

gather is a noun but fort up is not a noun.

Word	Noun	Adjective	Verb	Adverb
gather	Yes	No	Yes	No
fort up	No	No	Yes	No

As verbs, fort up is a hyponym of gather; that is, fort up is a word with a more specific, narrower meaning than gather:

gather (noun)	fort up (noun)
the act of gathering something
sewing consisting of small folds or puckers made by pulling tight a thread in a line of stitching

gather (verb)	fort up (verb)
increase in amount by collecting or gathering	gather in, or as if in, a fort, as for protection or defense
increase or develop
conclude from evidence
assemble or get together
draw together into folds or puckers
look for (food) in nature
draw and bring closer
collect in one place
get people together