hem vs sew

hem is a noun but sew is not a noun.

Word	Noun	Adjective	Verb	Adverb
hem	Yes	No	Yes	No
sew	No	No	Yes	No

As verbs, sew is a hypernym of hem; that is, sew is a word with a broader meaning than hem:

Other hypernyms of hem include run up, sew together, stitch.

hem (noun)	sew (noun)
the edge of a piece of cloth; especially the finished edge that has been doubled under and stitched down
the utterance of a sound similar to clearing the throat; intended to get attention, express hesitancy, fill a pause, hide embarrassment, warn a friend, etc.

hem (verb)	sew (verb)
utter `hem' or `ahem'	fasten by sewing; do needlework
fold over and sew together to provide with a hem	create (clothes) with cloth