sew vs hem

sew is not a noun while hem is a noun.

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

As verbs, hem is a hyponym of sew; that is, hem is a word with a more specific, narrower meaning than sew:

sew (noun)	hem (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.

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