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Webster 1913 Edition

Noun.

[Prob. from OF.

coustillier

groom or lad. Cf.

An inferior groom or lad employed by an esquire to carry the knight’s arms and other necessaries.

[Written also

coistrel

A mean, paltry fellow; a coward.

[Obs.]

Shak.

, n.

A coward; a runaway.

A young lad.

coistril ‎(plural coistrils)

(obsolete) An inferior groom or lad employed by an esquire to carry the knight's arms and other necessaries; a coistrel.
(obsolete) A mean, paltry fellow; a coward.
(Can we find and add a quotation of Shakespeare to this entry?)