Source : Webster's Revised Unabridged Dictionary (1913)

Trumpetweed \Trump"et*weed`\, n. (Bot.)
   (a) An herbaceous composite plant ({Eupatorium purpureum}),
       often having hollow stems, and bearing purplish flowers
       in small corymbed heads.
   (b) The sea trumpet.

Source : WordNet®

Eupatorium purpureum
     n : North American herb having whorled leaves and terminal
         clusters of flowers spotted with purple [syn: {Joe-Pye
         weed}, {purple boneset}, {trumpet weed}, {marsh milkweed}]