Is there a medieval term for sister/brother-in-law? The only example I could find was in GRR Martin's A Song of Ice and Fire series where he uses the terms goodsister and goodbrother. Are those rooted in actual medieval terms for in-laws? Were the in-laws even addressed as members of family with specific words? (I've read somewhere that before 19th century the in-laws were used instead of step-mother/father/etc., so they could not be used for the other relation or would be very confusing).

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    In answer to your comment in brackets, you may have it the wrong way round. A stepmother used to be called a mother-in-law (e.g. in Dickens' Pickwick Papers), presumably because the relationship was created by a marriage, though in this case one's father's not one's own. Commented Jun 30, 2018 at 7:41
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    By the way, the term goodsister is probably a loan translation from French belle-soeur, "sister in law". Dutch borrowed the same word (with the same meaning) as schoonzuster. Belle = schoon = "beautiful, nice". Oddly, bonne-soeur ("good sister") is used for nuns. So perhaps the English translation is based on an older use of bonne-soeur, or Englishmen at the time confused belle-soeur with bonne-soeur. Commented Jun 30, 2018 at 12:57
  • "sister's husband" etc also seem common.
    – Stuart F
    Commented Sep 16, 2023 at 8:17

2 Answers 2


According to the Oxford English Dictionary, they have been called in laws for a while. Here are its earliest examples of each:

Later, in the 1530 Tyndale Bible (a little too late for it to be considered medieval) shortened versions of these terms, sister law and brother law, were used (again, the earliest examples I could find in the OED):

Yf the man will not take his systerlawe, then let her goo to the gate vnto the elders and saye: My brotherlawe..will not marie me.

Confusingly enough, sometimes they are simply referred to as brother and sister according to the OED:

In addition, good brother and good sister were used, but mainly in Scottish English. The OED's earliest respective citations are:

  • Iames steward, that ledar was Eftir his gud brother disses.
    The Bruce, 1375

  • That his gud systyr the Quenys grace be nocht therby mynyst in hyr autorite.
    Douglas Book, 1515


Brother-in-law in English is tacor and sister-in-law is doomsister. Father-in-law is swēor and mother-in-law is sweġer.

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  • Well, the Normans conquered England, so a lot of "foreign" words have entered English from Old French. But sister-in-law and brother-in-law are both made of Anglo-Saxon words.
    – TimR
    Commented Sep 15, 2023 at 1:28
  • No, they are a combination of Old English and Old Norse. Law is Old Norse, doom is the same in Old English. If sister-in-law and brother-in-law were all English they would be something like doombrother (tacor) and doomsister. Commented Sep 16, 2023 at 11:51

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