/pleuh nair"ee euhn/ , n. Zool.
any of various free-swimming, mostly freshwater flatworms of the class Turbellaria, having an undulating or sluglike motion: popular in laboratory studies for the ability to regenerate lost parts.
[ 1885-60; Planari ( a ) a flatworm genus (n. use of fem. of LL planarius level, on level ground; taken to mean "flat"; see PLANE 1 , -ARY + -AN ]