ple·on \ˈplēˌän\noun (-s) Etymology: New Latin, from Greek pleōn, present participle of plein to sail; from the fact that it bears the swimming limbs — more at flow 1.: the abdomen of a crustacean 2.: the telson of a king crab • ple·o·nal\-ēənəl\orple·on·ic\(ˈ)plē|änik\adjective