daydream vs envisage

daydream is a noun but envisage is not a noun.

Word	Noun	Adjective	Verb	Adverb
daydream	Yes	No	Yes	No
envisage	No	No	Yes	No

As verbs, envisage is a hypernym of daydream; that is, envisage is a word with a broader meaning than daydream:

daydream: have a daydream; indulge in a fantasy
envisage: form a mental image of something that is not present or that is not the case

Other hypernyms of daydream include conceive of, ideate, imagine.

daydream (noun)	envisage (noun)
absentminded dreaming while awake

daydream (verb)	envisage (verb)
have a daydream; indulge in a fantasy	form a mental image of something that is not present or that is not the case
have dreamlike musings or fantasies while awake