Probably from Old French coustillier groom or lad. Compare custrel.
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.
c. 1592, Shakespeare, William; Anonymous, Arden of Faversham, Act 3, Scene 2:
- And he shall 'by his merriment as dear / As ever coistril bought so little sport: / Ne'er let this sword assist me when I need, / But rust and canker after I have sworn.
c. 1601–1602, Shakespeare, William, Twelfth Night, Act 1, Scene 3:
- He's a coward and a coistril that will not / drink to my niece till his brains turn o'the toe like a / parish top.