The building blocks of English

Affixes

terato-

Monsters or abnormal forms.

Greek teras, terat‑, monster.

Though teratology can be a collection of tales about fantastic creatures and monsters, it is also the scientific study of congenital abnormalities and abnormal formations. Most terms in terato‑ have this medical sense, as in teratogenesis, the process by which congenital malformations are produced in an embryo or fetus, such as by a teratogen; a teratoma is a tumour composed of tissues not normally present at the site; a teratocarcinoma is a form of malignant teratoma occurring especially in the testis.