1660s, from French toxique and directly from Late Latin toxicus "poisoned," from Latin toxicum "poison," from Greek toxikon (pharmakon) "(poison) for use on arrows," from toxikon, neuter of toxikos "pertaining to arrows or archery," and thus to a bow, from toxon "bow," probably from a Scythian word that also was borrowed into Latin as taxus "yew." Watkins suggests a possible source in Iranian taxša- "bow," from PIE *tekw- "to run, flee." As a noun from 1890.