overhand vs overarm

overhand and overarm both are adjectives.

Word	Noun	Adjective	Verb	Adverb
overhand	No	Yes	No	No
overarm	No	Yes	No	No

As adjectives, overhand and overarm are synonyms defined as:

overhand and overarm: with hand brought forward and down from above shoulder level

Other synonyms of overhand include overhanded.

overhand (adjective)	overarm (adjective)
with hand brought forward and down from above shoulder level	with hand brought forward and down from above shoulder level
sewn together with overhand stitches (close vertical stitches that pass over and draw the two edges together)