We don't have synonyms for coistrel yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are cloistral, costrel and coystrel.
(n) :
Alternative form of custrel. [A knight's attendant or man-at-arms; a knave.]
(n) :
Alternative form of coistril. [(obsolete) An inferior groom or lad employed by an esquire to carry the knight's arms and other necessaries; a coistrel.]
(n) :
Alternative form of custrel. [A knight's attendant or man-at-arms; a knave.]
(n) :
Alternative form of coistril. [(obsolete) An inferior groom or lad employed by an esquire to carry the knight's arms and other necessaries; a coistrel.]