dietitian vs specializer

dietitian and specializer both are nouns.

Word	Noun	Adjective	Verb	Adverb
dietitian	Yes	No	No	No
specializer	Yes	No	No	No

As nouns, specializer is a hypernym of dietitian; that is, specializer is a word with a broader meaning than dietitian:

dietitian: a specialist in the study of diet and nutrition
specializer: an expert who is devoted to one occupation or branch of learning

Other hypernyms of dietitian include specialiser, specialist.

dietitian (noun)	specializer (noun)
a specialist in the study of diet and nutrition	an expert who is devoted to one occupation or branch of learning