specialise vs expatiate

specialise and expatiate both are verbs.

Word	Noun	Adjective	Verb	Adverb
specialise	No	No	Yes	No
expatiate	No	No	Yes	No

As verbs, expatiate is a hypernym of specialise; that is, expatiate is a word with a broader meaning than specialise:

specialise: be specific about
expatiate: add details, as to an account or idea; clarify the meaning of and discourse in a learned way, usually in writing

Other hypernyms of specialise include dilate, elaborate, enlarge, expand, exposit, expound, flesh out, lucubrate.

specialise (verb)	expatiate (verb)
become more focused on an area of activity or field of study	add details, as to an account or idea; clarify the meaning of and discourse in a learned way, usually in writing
suit to a special purpose
evolve so as to lead to a new species or develop in a way most suited to the environment
be specific about
devote oneself to a special area of work