dimmer vs rheostat

dimmer and rheostat both are nouns.

Word	Noun	Adjective	Verb	Adverb
dimmer	Yes	No	No	No
rheostat	Yes	No	No	No

As nouns, rheostat is a hypernym of dimmer; that is, rheostat is a word with a broader meaning than dimmer:

dimmer: a rheostat that varies the current through an electric light in order to control the level of illumination
rheostat: resistor for regulating current

Other hypernyms of dimmer include variable resistor.

dimmer (noun)	rheostat (noun)
a rheostat that varies the current through an electric light in order to control the level of illumination	resistor for regulating current