tension vs mental strain

tension and mental strain both are nouns.

Word	Noun	Adjective	Verb	Adverb
tension	Yes	No	No	No
mental strain	Yes	No	No	No

As nouns, mental strain is a hypernym of tension; that is, mental strain is a word with a broader meaning than tension:

Other hypernyms of tension include nervous strain, strain.

tension (noun)	mental strain (noun)
the action of stretching something tight	(psychology) nervousness resulting from mental stress
(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