idea vs guessing

idea and guessing both are nouns.

Word	Noun	Adjective	Verb	Adverb
idea	Yes	No	No	No
guessing	Yes	No	No	No

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

idea (noun)	guessing (noun)
the content of cognition; the main thing you are thinking about	an estimate based on little or no information
your intention; what you intend to do
an approximate calculation of quantity or degree or worth
a personal view
(music) melodic subject of a musical composition