From The Collaborative International Dictionary of English v.0.48 [gcide]:
Castling \Cast"ling\, n.
That which is cast or brought forth prematurely; an abortion.
--Sir T. Browne.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Castling \Cas"tling\, n. (Chess)
A compound move of the king and castle. See Castle, v. i.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Castle \Cas"tle\, v. i. [imp. & p. p. Castled; p. pr. & vb. n.
Castling.] (Chess)
To move the castle to the square next to king, and then the
king around the castle to the square next beyond it, for the
purpose of covering the king.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
castling
n 1: interchanging the positions of the king and a rook [syn:
castle, castling]