optical disk vs optical disc

optical disk and optical disc both are nouns.

Word	Noun	Adjective	Verb	Adverb
optical disk	Yes	No	No	No
optical disc	Yes	No	No	No

As nouns, optical disk and optical disc are synonyms defined as:

optical disk and optical disc: a disk coated with plastic that can store digital data as tiny pits etched in the surface; is read with a laser that scans the surface

optical disk (noun)	optical disc (noun)
a disk coated with plastic that can store digital data as tiny pits etched in the surface; is read with a laser that scans the surface	a disk coated with plastic that can store digital data as tiny pits etched in the surface; is read with a laser that scans the surface