Word Origin and History for semi-Expand before vowels sem-, word-forming element meaning half, part, partly; partial, imperfect; twice, from Latin semi-half, from PIE *semi-half (cf. Sanskrit sami half, Greek hemi-half, Old English sam-, Gothic sami-half).
Well-known rodents include mice, rats, squirrels, prairie dogs, porcupines, beavers, guinea pigs, hamsters, gerbils and capybaras. Other animals such as rabbits, hares, and pikas, whose incisors also grow continually, were once included with them, but are now considered to be in a separate order, the Lagomorpha.
(Incidentally, the Rodentia does not include rabbits; rabbits differ from rodents in having an extra pair of incisors and in other skeletal features. Rabbits, hares, and a few other species make up the Lagomorpha. Shrews, moles and hedgehogs are also not rodents; they are classified in the Insectivora.)