Source : Webster's Revised Unabridged Dictionary (1913)

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.