self-starter vs starter motor

self-starter and starter motor both are nouns.

Word	Noun	Adjective	Verb	Adverb
self-starter	Yes	No	No	No
starter motor	Yes	No	No	No

As nouns, starter motor is a hypernym of self-starter; that is, starter motor is a word with a broader meaning than self-starter:

self-starter: an electric starting motor that automatically starts an internal-combustion engine
starter motor: an electric motor for starting an engine

Other hypernyms of self-starter include starter, starting motor.

self-starter (noun)	starter motor (noun)
an electric starting motor that automatically starts an internal-combustion engine	an electric motor for starting an engine
an energetic person with unusual initiative