speculate vs mull

speculate is not a noun while mull is a noun.

Word	Noun	Adjective	Verb	Adverb
speculate	No	No	Yes	No
mull	Yes	No	Yes	No

As verbs, speculate and mull are synonyms defined as:

Other synonyms of speculate include chew over, contemplate, excogitate, meditate, mull over, muse, ponder, reflect, ruminate, think over.

speculate (noun)	mull (noun)
	a term used in Scottish names of promontories

speculate (verb)	mull (verb)
reflect deeply on a subject	reflect deeply on a subject
to believe especially on uncertain or tentative grounds	heat with sugar and spices to make a hot drink
talk over conjecturally, or review in an idle or casual way and with an element of doubt or without sufficient reason to reach a conclusion
invest at a risk