estimate vs guesswork

estimate and guesswork both are nouns.

Word	Noun	Adjective	Verb	Adverb
estimate	Yes	No	Yes	No
guesswork	Yes	No	No	No

As nouns, guesswork is a hyponym of estimate; that is, guesswork is a word with a more specific, narrower meaning than estimate:

estimate (noun)	guesswork (noun)
a judgment of the qualities of something or somebody	an estimate based on little or no information
an approximate calculation of quantity or degree or worth
the respect with which a person is held
a document appraising the value of something (as for insurance or taxation)
a statement indicating the likely cost of some job

estimate (verb)	guesswork (verb)
judge tentatively or form an estimate of (quantities or time)
judge to be probable