any old word rodent of the genus hystrix, having the back covered with long, sharp, erectile spines or quills, sometimes a foot long. the common species of europe and asia (hystrix cristata) is the best known.-any species of erethizon and related genera, native of america. they are related to the true porcupines, but have shorter spines, and are arboreal in their habits. the canada porcupine (erethizon dorsatus) is a well known species.