guess vs prognosticate

guess is a noun but prognosticate is not a noun.

Word	Noun	Adjective	Verb	Adverb
guess	Yes	No	Yes	No
prognosticate	No	No	Yes	No

As verbs, prognosticate is a hyponym of guess; that is, prognosticate is a word with a more specific, narrower meaning than guess:

Other hyponyms of guess include anticipate, call, forebode, foretell, predict, promise, surmise, suspect.

guess (noun)	prognosticate (noun)
an estimate based on little or no information
a message expressing an opinion based on incomplete evidence

guess (verb)	prognosticate (verb)
expect, believe, or suppose	make a prediction about; tell in advance
judge tentatively or form an estimate of (quantities or time)	indicate, as with a sign or an omen
guess correctly; solve by guessing
put forward, of a guess, in spite of possible refutation