ASPEN

[as.pen] n [ME, of an aspen, fr. asp aspen, fr. OE aespe; akin to OHG aspa aspen, Russ osina] (1596): any of several poplars (esp. Populus tremula of Europe and P. tremuloides and P. grandidentata of No. America) with leaves that flutter in the lightest wind because of their flattened petioles