twitching vs tic

twitching and tic both are nouns.

Word	Noun	Adjective	Verb	Adverb
twitching	Yes	No	No	No
tic	Yes	No	No	No

As nouns, tic is a hyponym of twitching; that is, tic is a word with a more specific, narrower meaning than twitching:

twitching: a sudden muscle spasm; especially one caused by a nervous condition
tic: a local and habitual twitching especially in the face

Other hyponyms of twitching include blepharism, fibrillation, fasciculation.

twitching (noun)	tic (noun)
a sudden muscle spasm; especially one caused by a nervous condition	a local and habitual twitching especially in the face