Water dock \Wa"ter dock`\ (Bot.) A tall, coarse dock growing in wet places. The American water dock is {Rumex orbiculatus}, the European is {R. Hydrolapathum}. Parella \Pa*rel"la\, Parelle \Pa`relle\, n. [Cf. F. parelle.] (Bot.) (a) A name for two kinds of dock ({Rumex Patientia} and {R. Hydrolapathum}). (b) A kind of lichen ({Lecanora parella}) once used in dyeing and in the preparation of litmus.