chance upon vs regain

chance upon and regain both are verbs.

Word	Noun	Adjective	Verb	Adverb
chance upon	No	No	Yes	No
regain	No	No	Yes	No

As verbs, regain is a hypernym of chance upon; that is, regain is a word with a broader meaning than chance upon:

chance upon: find unexpectedly
regain: come upon after searching; find the location of something that was missed or lost

Other hypernyms of chance upon include find.

chance upon (verb)	regain (verb)
find unexpectedly	get or find back; recover the use of
	come upon after searching; find the location of something that was missed or lost