What does STRAIN mean?

noun

1. (physics) deformation of a physical body under the action of applied forces
2. difficulty that causes worry or emotional tension“she endured the stresses and strains of life”
3. a succession of notes forming a distinctive sequence“she was humming an air from Beethoven”
4. (psychology) nervousness resulting from mental stress“his responsibilities were a constant strain”
5. a special variety of domesticated animals within a species“he experimented on a particular breed of white rats”
6. (biology) a group of organisms within a species that differ in trivial ways from similar groups“a new strain of microorganisms”
7. injury to a muscle (often caused by overuse); results in swelling and pain
8. the general meaning or substance of an utterance“although I disagreed with him I could follow the tenor of his argument”