Definition of "pill bug" [pill bug]

• A small terrestrial isopod crustacean of the genus Armadillidium closely related to the sow bug and having a convex, segmented, flexible body enabling it to curl into a ball when disturbed. In this sense also called roly-poly. (noun)
• A sow bug. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.