round shape vs disk

round shape and disk both are nouns.

Word	Noun	Adjective	Verb	Adverb
round shape	Yes	No	No	No
disk	Yes	No	Yes	No

As nouns, disk is a hyponym of round shape; that is, disk is a word with a more specific, narrower meaning than round shape:

round shape (noun)	disk (noun)
a shape that is curved and without sharp angles	a flat circular plate
	sound recording consisting of a disk with a continuous groove; used to reproduce music by rotating while a phonograph needle tracks in the groove
	(computer science) a memory device consisting of a flat disk covered with a magnetic coating on which information is stored
	something with a round shape resembling a flat circular plate

round shape (verb)	disk (verb)
	draw a harrow over (land)