Main Entry: as·pen

Pronunciation: \ˈas-pən\

Function: noun

Etymology: Middle English, of an aspen, from asp aspen, from Old English æspe; akin to Old High German aspa aspen, Russian osina

Date: 1593

: any of several poplars (especially Populus tremula of Europe and P. tremuloides and P. grandidentata of North America) with leaves that flutter in the lightest wind because of their flattened petioles