brother-in-law

from WordNet (r) 3.0 (2006)

brother-in-law
    n 1: a brother by marriage

from The Collaborative International Dictionary of English v.0.48

Brother-in-law \Broth"er-in-law`\, n.; pl. {Brothers-in-law}.
   The brother of one's husband or wife; also, the husband of
   one's sister; sometimes, the husband of one's wife's sister.
   [1913 Webster]

from Bouvier's Law Dictionary, Revised 6th Ed (1856)

BROTHER-IN-LAW, domestic relat. The brother of a wife, or the husband of a 
sister. There is no relationship, in the former case, between the husband 
and the brother-in-law, nor in the latter, between the brother and the 
husband of the sister; there is only affinity between them. See Vaughan's 
Rep. 302, 329.

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