Word Study
Trilobite
CIDE DICTIONARY
Trilobite, n. [Cf. F. trilobite. See Trilobate.].
Any one of numerous species of extinct arthropods belonging to the order Trilobita. Trilobites were very common in the Silurian and Devonian periods, but became extinct at the close of the Paleozoic. So named from the three lobes usually seen on each segment. [1913 Webster]
OXFORD DICTIONARY
Trilobite, n. any fossile marine arthropod of the class Trilobita of Palaeozoic times, characterized by a three-lobed body.
Etymology
mod.L Trilobites (as TRI-, Gk lobos lobe)
For further exploring for "Trilobite" in Webster Dictionary Online