1. an extinct arthropod that was abundant in Paleozoic times
; had an exoskeleton divided into three parts
The Collaborative International Dictionary of English v.0.48:
Trilobite \Tri"lo*bite\ (tr[imac]"l[-o]*b[imac]t), n. [Cf. F.
trilobite. See Trilobate.] (Paleon.)
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.
WordNet (r) 3.0 (2006):
n 1: an extinct arthropod that was abundant in Paleozoic times;
had an exoskeleton divided into three parts