/euh sid"ee euhn/ , Zool.
n.
1. any solitary or colonial tunicate of the class Ascidiacea, exhibiting in the larval stage the vertebrate characteristics of a notocord and hollow nerve cord.
adj.
2. belonging or pertaining to the class Ascidiacea.
[ 1855-60; Ascidi ( um ) a tunicate genus (see ASCIDIUM) + -AN ]