stretching vs tension

stretching and tension both are nouns.

Word	Noun	Adjective	Verb	Adverb
stretching	Yes	No	No	No
tension	Yes	No	No	No

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

Other hyponyms of stretching include extension.

stretching (noun)	tension (noun)
exercise designed to extend the limbs and muscles to their full extent	the action of stretching something tight
act of expanding by lengthening or widening	(physics) a stress that produces an elongation of an elastic physical body
	feelings of hostility that are not manifest
	the physical condition of being stretched or strained
	a balance between and interplay of opposing elements or tendencies (especially in art or literature)
	(psychology) a state of mental or emotional strain or suspense