early 14c., "feebleness, weariness," from faint (adj.) + -ness. Meaning "exhaustion" is mid-15c. Of color, light, etc., from 1640s.
Entries linking to faintness
faint adj.
c. 1300, "enfeebled; wearied, exhausted," from Old French faint, feint "false, deceitful; sham, artificial; weak, faint, lazy, indolent, cowardly," past participle of feindre "hesitate, falter, be indolent, show weakness, avoid one's duty by pretending," from Latin fingere "to touch, handle; devise; fabricate, alter, change" (from PIE root *dheigh- "to form, build"). Also from c. 1300 as "deceitful; unreliable; false." Meaning "wanting in spirit or courage, cowardly" (a sense now mostly encountered in faint-hearted) is from early 14c. From early 15c. of actions, functions, colors, etc., "weak, feeble, poor." Meaning "producing a feeble impression upon the senses" is from 1650s.
-ness
word-forming element denoting action, quality, or state, attached to an adjective or past participle to form an abstract noun, from Old English -nes(s), from Proto-Germanic *in-assu- (cognates: Old Saxon -nissi, Middle Dutch -nisse, Dutch -nis, Old High German -nissa, German -nis, Gothic -inassus), from *-in-, originally belonging to the noun stem, + *-assu-, abstract noun suffix, probably from the same root as Latin -tudo (see -tude).