theoretician vs theoriser

theoretician and theoriser both are nouns.

Word	Noun	Adjective	Verb	Adverb
theoretician	Yes	No	No	No
theoriser	Yes	No	No	No

As nouns, theoretician and theoriser are synonyms defined as:

theoretician and theoriser: someone who theorizes (especially in science or art)

Other synonyms of theoretician include idealogue, theorist, theorizer.

theoretician (noun)	theoriser (noun)
someone who theorizes (especially in science or art)	someone who theorizes (especially in science or art)