tablet computer vs computer

tablet computer and computer both are nouns.

Word	Noun	Adjective	Verb	Adverb
tablet computer	Yes	No	No	No
computer	Yes	No	No	No

As nouns, computer is a hypernym of tablet computer; that is, computer is a word with a broader meaning than tablet computer:

tablet computer (noun)	computer (noun)
a portable computer with a touchscreen	a machine for performing calculations automatically
	an expert at calculation (or at operating calculating machines)