/pi per"euh nal', puy-, pip"euhr euh-/ , n. Chem.
a white, crystalline, water-insoluble aldehyde, C 8 H 6 O 3 , which darkens on exposure to light: used chiefly in perfumery and organic synthesis. Also called piperonyl aldehyde, heliotropin .
[ 1865-70; PIPER(INE) + -ONE + -AL 1 ]