teratogen te·rat·o·gen (tə-rāt'ə-jən, těr'ə-tə-)
n.
An agent, such as a virus, a drug, or radiation, that causes malformation of an embryo or a fetus.
teratogenic ter·a·to·gen·ic (těr'ə-tə-jěn'ĭk)
adj.
Of, relating to, or causing malformations of an embryo or a fetus.