Coistril \Cois"tril\, n. [Prob. from OF. coustillier groom or lad. Cf. {Custrel}.] 1. An inferior groom or lad employed by an esquire to carry the knight's arms and other necessaries. [Written also {coistrel}.] 2. A mean, paltry fellow; a coward. [Obs.] --Shak.