Etymology
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stability (n.)

mid-14c., "firmness of resolve, mental equilibrium" (of persons), from Old French stablete, establete "firmness, solidity, stability; durability, constancy" (Modern French stabilité), from Latin stabilitatem (nominative stabilitas) "a standing fast, firmness," figuratively "security, steadfastness," from stabilis "steadfast, firm" (see stable (adj.)). In physical sense, "state of being difficult to overthrow, power of remaining upright," it is recorded from early 15c. Meaning "continuance in the same state" is from 1540s.

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fortitudinous (adj.)

"capable of endurance," 1752, from Latin fortitudinem (nominative fortitudo) "strength, firmness" (see fortitude) + -ous. Related: Fortitudinously.

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solidity (n.)

late 14c., solidite, "firmness, hardness," from Old French solidite (Modern French solidité) or directly from Latin soliditatem (nominative soliditas) "solidness, firmness, a solid mass," from solidus "firm, whole, undivided" (see solid (adj.)). The meaning "state or quality of being materially solid" is from c. 1600.

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resolve (n.)

"determination, firmness or fixedness of purpose; a determination," 1590s, from resolve (v.).  Meaning "a determination of a deliberative body" is from 1650s.

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backbone (n.)

"spine, vertebral column," early 14c., from back (n.) + bone (n.). The figurative sense of "firmness of purpose, strength of character" is by 1843.

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soundness (n.)

late 14c., soundnes, "solidity, firmness," from sound (adj.) + -ness. Of the mind, etc. by 1540s.

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fortitude (n.)

late 14c., "moral strength (as a cardinal virtue); courage," from Latin fortitudo "strength, force, firmness, manliness," from fortis "strong, brave" (see fort). From early 15c. as "physical strength."

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constance (n.)

obsolete form of constancy, mid-14c., constaunce, "steadfastness, self-possession, composure," from Old French constance "steadfastness, permanence" (14c.), from Latin constantia "firm standing, steadiness, firmness, unchangeableness; firmness of character" (source of Italian costanza, Spanish constancia), abstract noun from present-participle stem of constare "to stand together" (see constant (adj.)). Obsolete since 17c. except as a given name for a girl (familiarly Connie), in which use it enjoyed a mild popularity in U.S. c. 1945-1955.

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fastness (n.)

"a place not easily forced, a stronghold," late Old English fæstnes "firmness, strongness, massiveness, stability; the firmament," from fast (adj.) in its older sense of "firm, fixed in place" + -ness.

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limp (adj.)

"flaccid, drooping, lacking stiffness or firmness," 1706, of obscure origin, apparently from the first element in Old English lemphealt (see limp (v.)). Related: Limply; limpness. A limp wrist as indicative of male effeminate homosexuality is from 1960.

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