excogitate vs mull over

excogitate and mull over both are verbs.

Word	Noun	Adjective	Verb	Adverb
excogitate	No	No	Yes	No
mull over	No	No	Yes	No

As verbs, excogitate and mull over are synonyms defined as:

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

excogitate (verb)	mull over (verb)
reflect deeply on a subject	reflect deeply on a subject
come up with (an idea, plan, explanation, theory, or principle) after a mental effort