supposal vs fundament

supposal and fundament both are nouns.

Word	Noun	Adjective	Verb	Adverb
supposal	Yes	No	No	No
fundament	Yes	No	No	No

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

supposal: a hypothesis that is taken for granted
fundament: the fundamental assumptions from which something is begun or developed or calculated or explained

supposal (noun)	fundament (noun)
a hypothesis that is taken for granted	lowest support of a structure
the cognitive process of supposing	the fleshy part of the human body that you sit on
	the fundamental assumptions from which something is begun or developed or calculated or explained