Etymology
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invalid (adj.2)
"of no legal force," 1630s, from special use of Latin invalidus "not strong, infirm, impotent, feeble, inadequate," from in- "not" (see in- (1)) + validus "strong" (from PIE root *wal- "to be strong").
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valid (adj.)

1570s, "having force in law, legally binding," from French valide (16c.), from Latin validus "strong, effective, powerful, active," from valere "be strong" (from PIE root *wal- "to be strong"). The meaning "sufficiently supported by facts or authority, well-grounded" is first recorded 1640s.

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invalid (adj.1)
"not strong, infirm," also "infirm from sickness, disease, or injury", 1640s, from Latin invalidus "not strong, infirm, impotent, feeble, inadequate," from in- "not" (see in- (1)) + validus "strong" (from PIE root *wal- "to be strong"). With pronunciation from French invalide (16c.).
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valediction (n.)
"a farewell, a bidding farewell," 1610s, from past participle stem of Latin valedicere "bid farewell, take leave," from vale "farewell!," second person singular imperative of valere "be well, be strong" (from PIE root *wal- "to be strong") + dicere "to say" (from PIE root *deik- "to show," also "pronounce solemnly").
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prevalent (adj.)

early 15c., "having great power or force, controlling, ruling," from Latin praevalentem (nominative praevalens) "of superior strength; mighty," present participle of praevalere "to be more able," from prae "before" (see pre-) + valere "have power, be strong" (from PIE root *wal- "to be strong"). Meaning "widespread, extensively existing, in general use" is from 1650s.

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prevalence (n.)

1590s, "fact of having mastery," from French prévalence (15c.), from Medieval Latin praevalentia "superior force," from Latin praevalens, present participle of praevalere "to be more able," from prae "before" (see pre-) + valere "have power, be strong" (from PIE root *wal- "to be strong"). Meaning "condition of being widespread or general" is from 1713. Shakespeare has prevailment.

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valence (n.)
early 15c., "extract, preparation," from Latin valentia "strength, capacity," from valentem (nominative valens) "strong, stout, vigorous, powerful," present participle of valere "be strong" (from PIE root *wal- "to be strong"). Chemistry sense of "relative combining capacity of an element with other atoms when forming compounds or molecules" is recorded from 1884, from German Valenz (1868), from the Latin word. Related: Valency.
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evaluation (n.)
1755, "action of appraising or valuing," from French évaluation, noun of action from évaluer "to find the value of," from é- "out" (see ex-) + valuer, from Latin valere "be strong, be well; be of value, be worth" (from PIE root *wal- "to be strong"). Meaning "job performance review" attested by 1947.
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valetudinarian (n.)
"one who is constantly concerned with his own ailments," 1703, from valetudinary (1580s), from Latin valetudinarius, from valetudo "state of health" (either good or bad), from valere "be strong" (from PIE root *wal- "to be strong") + -tudo, abstract noun suffix (see -tude). Valetudinary (adj.) "sickly" is recorded from 1580s.
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equivalent (adj.)

early 15c., "equal in value, power, or effect," from Late Latin aequivalentem (nominative aequivalens) "equivalent," present participle of aequivalere "be equivalent," from Latin aequus "equal" (see equal (adj.)) + valere "be well, be worth" (from PIE root *wal- "to be strong"). As a noun from c. 1500, "that which is equal or corresponds to." Related: Equivalently.

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