pso·ra·len 
(sôrə-lən)
(sôrə-lən)n.
Any of a group of chemical compounds found in certain plants, used to treat psoriasis and vitiligo.
[From New Latin Psōralea, plant genus, from Greek psōralea, neuter pl. of psōraleos, mangy (from the appearance of the plants' leaves), from psōrā, itch.]