The Collaborative International Dictionary of English v.0.48:

Inlaw \In*law"\, v. t. [In + law. Cf. Inlagation.] (Old Eng.
   Law)
   To clear of outlawry or attainder; to place under the
   protection of the law. --Burrill.

The Collaborative International Dictionary of English v.0.48:

in-law \in"-law`\, n.
   A person who is related by marriage, as distinguished from a
   blood relative; esp. mother-in-law (the mother of one's
   spouse), father-in-law (the father of one's spouse),
   brother-in-law (the brother of one's spouse, or husband of
   one's spouse's sister), sister-in-law (the sister of one's
   spouse, or wife of one's spouse's brother).
   [PJC]

The Collaborative International Dictionary of English v.0.48:

-in-law \-in"-law`\, suff.
   A suffix meaning through marriage. See in-law.
   [PJC]

WordNet (r) 3.0 (2006):

in-law
    n 1: a relative by marriage [syn: in-law, relative-in-law]