means the quality of having little weight, or of being free from heaviness, whether physical, emotional, or in tone.

from From Old English 'liht' (not heavy) plus the noun-forming suffix '-ness'. 'Liht' traces back to a Proto-Germanic root shared with German 'leicht' and is a likely cousin of Latin 'levis' (light, of low weight) — the same family that gives us 'levity' and 'levitate'. Worth noting: the 'light' of brightness ('leoht' in Old English) is a separate word from a different root, though centuries of spelling collapsed them into the same five letters.