Origin and history of wan-

Old English wann "dark, dusky, lacking luster," of weather, water, etc.; c. 1300, "leaden, pale, gray" through disease or distress; according to Boutkan related to Old English wanian "make or become smaller gradually, diminish, decline, fade" (see wane).

The connecting notion is want of vivid coloration, hence its use of anything indeterminately grayish or of a gloomy, unwholesome look. It also sometimes was used of bruises (compare livid). By mid-14c. of heavenly bodies. Related: Wanly; wanness.

Middle English wannen, "decrease, be diminished," especially of the periodic lessening of the visible moon, from Old English wanian "make or become smaller gradually, diminish, decline, fade," from Proto-Germanic *wanōnan (source also of Old Saxon wanon, Old Norse vana, Old Frisian wania, Middle Dutch waenen, Old High German wanon "to wane, to grow less").

This is reconstructed to be from PIE *weno-, suffixed form of root *eue- "to leave, abandon, give out." Also compare wan (adj.).Related: Waned; waning; wanes.

As a noun, "periodic waning of the moon," 1560s; the Old English noun sense of "shortage, lack" is obsolete except in some technical uses. In Old English, Middle English wane also was an adjective, with numbers, "(one or two) short of," as in one wane of a hundred "99."