PC vs desktop computer

PC and desktop computer both are nouns.

Word	Noun	Adjective	Verb	Adverb
PC	Yes	No	No	No
desktop computer	Yes	No	No	No

As nouns, desktop computer is a hyponym of PC; that is, desktop computer is a word with a more specific, narrower meaning than PC:

PC: a small digital computer based on a microprocessor and designed to be used by one person at a time
desktop computer: a personal computer small enough to fit conveniently in an individual workspace

Other hyponyms of PC include portable computer.

PC (noun)	desktop computer (noun)
a small digital computer based on a microprocessor and designed to be used by one person at a time	a personal computer small enough to fit conveniently in an individual workspace