helix vs double helix

helix and double helix both are nouns.

Word	Noun	Adjective	Verb	Adverb
helix	Yes	No	No	No
double helix	Yes	No	No	No

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

helix: a curve that lies on the surface of a cylinder or cone and cuts the element at a constant angle
double helix: a pair of parallel helices intertwined about a common axis

helix (noun)	double helix (noun)
a structure consisting of something wound in a continuous series of loops	a pair of parallel helices intertwined about a common axis
a curve that lies on the surface of a cylinder or cone and cuts the element at a constant angle