sow bug

1. Any of various small terrestrial isopod crustaceans, chiefly of the genera Oniscus and Porcellio, commonly found under logs or stones and having an oval, segmented body.
2. A pill bug. See Usage Note at pill bug.

[From its piglike shape.]

(click to enlarge)
Sow bug (Oniscus asellus). (credit: Hugh Spencer)

Any of certain terrestrial crustaceans of the order Isopoda, especially members of the genus Oniscus. Native to Europe, they have been introduced into North America. Sow bugs grow to 0.7 in. (18 mm) long. The oval, gray body is rather arched and is covered with broad, armourlike plates. Two elbowed antennae extend about half the length of the body, and there are seven pairs of limbs. The sow bug lives in moist places, especially under stones, in moist leaf litter, and in cellars. See also pill bug.

For more information on sow bug, visit Britannica.com.

The noun has one meaning:

Meaning #1: terrestrial isopod having an oval segmented body (a shape like a sow)