speech synthesizer vs device

speech synthesizer and device both are nouns.

Word	Noun	Adjective	Verb	Adverb
speech synthesizer	Yes	No	No	No
device	Yes	No	No	No

As nouns, device is a hypernym of speech synthesizer; that is, device is a word with a broader meaning than speech synthesizer:

speech synthesizer: a device used for artificial production of human speech.
device: an instrumentality invented for a particular purpose

speech synthesizer (noun)	device (noun)
a device used for artificial production of human speech.	any clever maneuver
	an instrumentality invented for a particular purpose
	an emblematic design (especially in heraldry)
	any ornamental pattern or design (as in embroidery)
	something in an artistic work designed to achieve a particular effect