I found this website that has an analysis of the "relationship" question on the US Census over time.
It appears that, since the 1890s, the term "partner" was used as one of several descriptions in the census relationship column to indicate a boarder. The article is quite interesting. It is an analysis of people who are considered boarders in the households in census records from 1890 to the 2000s.
--- In firstname.lastname@example.org, "Walt/Gloria Elston" <elstonwg@...> wrote:
> I came across something in the 1940 US Federal Census that I have never
> seen before. In the entry for one household, one gentleman was listed as
> head of household and the other gentleman was listed as "partner". In
> today's language the word might mean something other than what it meant in
> 1940. Anyone see this notation in their research? I am thinking that in
> 1940 it might have meant that the two were equal head of household
> (each splitting the rent etc.).
> [Non-text portions of this message have been removed]