work on vs rework

work on and rework both are verbs.

Word	Noun	Adjective	Verb	Adverb
work on	No	No	Yes	No
rework	No	No	Yes	No

As verbs, rework is a hyponym of work on; that is, rework is a word with a more specific, narrower meaning than work on:

Other hyponyms of work on include hot-work, cold work, coldwork, overwork, make over, retread, rack, tool, till.

work on (verb)	rework (verb)
shape, form, or improve a material	use again in altered form
to exert effort in order to do, make, or perform something