Definition of "fers"

With their introduction the fers and the alfil disappeared from European chess.

1898 January, A. A. McDonald, “The Origin and Early History of Chess”, in Journal of the Royal Asiatic Society‎, volume 30, number 1, London: Royal Asiatic Society, page 138

In the Chronique of Philip Mouskat (a.d. 1243), lines 23617–20, is a reference to a king of Fierges, indicating that a fers could be promoted to a king at this early period.

1979 , R. C. Bell, “War Games”, in Board and Table Games from Many Civilizations‎, 2nd edition, New York: Dover Publications, page 71

This fers mates him in straight lines; this fers mates him at an angle.

2015 September, Nancy Marie Brown, Ivory Vikings: The Mystery of the Most Famous Chessmen in the World and the Woman Who Made Them‎, New York: St. Martin's Press, page 112