Entry 1 sense Webster, 1913 blueweed · blue·weed · IPA 01 n. a coarse prickly European weed (Echium vulgare) with spikes of blue flowers; naturalized in the U. S. 1. a coarse prickly European weed (Echium vulgare) with spikes of blue flowers; naturalized in the U. S. Syn. blue devil, blue thistle, viper's bugloss.