The story
From waxing + moon. Compare Middle English wexinge of the mone, þe waxyng of moone, waxinge of þe mone, wexinge of þe mone (literally “(the) waxing of the moon”).
Etymology from Wiktionary, CC BY-SA 4.0.
waxing moon
Today it means: A moon (usually the Moon, that is, Earth's moon) when it appears larger each night as it progresses from a new moon to a full moon: a moon in any of the increasing lunar phases. Full definition →