1540s, from French validité or directly from Late Latin validitatem (nominative validitas) "strength," from Latin validus (see valid).
mid-15c., "food or medicine which restores health or strength," from restorative (adj.), or from Medieval Latin restaurativum "a restorative," noun use of the neuter of restorativus.
early 15c., puissaunce, "power, strength, authority," from Old French puissance, poissance "power, might" (12c.), from puissant (see puissant).
Old English mægen (Mercian megen) "power, bodily strength; force, violent effort; strength of mind or will; efficacy; supernatural power," from Proto-Germanic *maginam "power" (source also of Old High German megin "strength, power, ability"), suffixed form of PIE root *magh- "to be able, have power."
Original sense of "power" is preserved in phrase might and main. Also used in Middle English for "royal power or authority" (c. 1400), "military strength" (c. 1300), "application of force" (c. 1300). Meaning "chief or main part" (c. 1600) now is archaic or obsolete. Meaning "principal duct, pipe, or channel in a utility system" is first recorded 1727 in main drain.
Used since 1540s for "continuous stretch of land or water;" in nautical jargon used loosely for "the ocean," but in Spanish Main the word is short for mainland and refers to the coast between Panama and Orinoco (as contrasted to the islands of the West Indies).
1913, "to accomplish by strength," from muscle (n.). Meaning "coerce by violence or pressure" is by 1929 in U.S. underworld slang. Related: Muscled; muscling.
"recovering strength and health after sickness," 1650s, from French convalescent, from Latin convalescentem (nominative convalescens), present participle of convalescere "thrive, regain health, begin to grow strong or well," from assimilated form of com-, here perhaps an intensive prefix (see com-), + valescere "to begin to grow strong," inchoative of valere "to be strong" (from PIE root *wal- "to be strong").
As a noun, "one who is recovering strength and health after sickness or debility," attested from 1758.