"study of marvels and monstrosities," 1842, from terato- + -logy. Earlier it meant "marvelous narrative" (1670s), from Greek teratologia "a telling of marvels." Related: Teratological; teratologist.
"the metaphysical science or study of being and the essence of things," 1660s (Gideon Harvey), from Modern Latin ontologia (c. 1600); see onto- + -logy. Related: Ontologist.
"study of the deformation of the flow of matter," 1929, from French rhéologie; see rheo- "current of a stream" + -logy "study of." Related: Rheologist; rheological.