circuit board vs plug-in

circuit board and plug-in both are nouns.

Word	Noun	Adjective	Verb	Adverb
circuit board	Yes	No	No	No
plug-in	Yes	No	No	No

As nouns, circuit board and plug-in are synonyms defined as:

circuit board and plug-in: a printed circuit that can be inserted into expansion slots in a computer to increase the computer's capabilities

Other synonyms of circuit board include add-in, board, card, circuit card.

circuit board (noun)	plug-in (noun)
a printed circuit that can be inserted into expansion slots in a computer to increase the computer's capabilities	a printed circuit that can be inserted into expansion slots in a computer to increase the computer's capabilities
	a software module that extends or enhances the capabilities of an existing application