winterbadger | Boston marriage

In the 19th century, this term was used for households where two women lived together, independent of any male support. Whether these were lesbian relationships -- in the sexual sense -- is debatable and debated. The likelihood is that some were, some weren't. Today, the term "Boston marriage" is sometimes used for lesbian relationships -- two women living together -- which are not sexual.

from about.com; see also this article on the excellent celebratefriendship site.

I came across this phrase many, many years ago, and was using it just this morning in (email) conversation and was struck by how apt it has now become. :-)