disc brake vs disk brake

disc brake and disk brake both are nouns.

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

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

disc brake and disk brake: hydraulic brake in which friction is applied to both sides of a spinning disk by the brake pads

disc brake (noun)	disk brake (noun)
hydraulic brake in which friction is applied to both sides of a spinning disk by the brake pads	hydraulic brake in which friction is applied to both sides of a spinning disk by the brake pads