overstock vs stock up

overstock and stock up both are verbs.

Word	Noun	Adjective	Verb	Adverb
overstock	No	No	Yes	No
stock up	No	No	Yes	No

As verbs, stock up is a hypernym of overstock; that is, stock up is a word with a broader meaning than overstock:

overstock: stock excessively
stock up: amass so as to keep for future use or sale or for a particular occasion or use

Other hypernyms of overstock include buy in, stock.

overstock (verb)	stock up (verb)
stock excessively	amass so as to keep for future use or sale or for a particular occasion or use