"Common-law wife" (or husband) is not a term I have heard in years. Partner is more usual. Before we got married, my husband always called me his ever-lovin'. He would put that on forms, much to people's confusion & amusement. And if you want awkward, the U.S. census in the 80s used POSSLQ: Persons of Opposite Sex Sharing Living Quarters.
Charles Osgood even wrote a poem on that acronym, with apologies to John Donne:
Come live with me and be my love,
And we will some new pleasures prove
Of golden sands and crystal brooks
With silken lines, and silver hooks.
There's nothing that I wouldn't do
If you would be my POSSLQ.
You live with me, and I with you,
And you will be my POSSLQ.
I'll be your friend and so much more;
That's what a POSSLQ is for.
And everything we will confess;
Yes, even to the IRS.
Some day on what we both may earn,
Perhaps we'll file a joint return.
You'll share my pad, my taxes, joint;
You'll share my life - up to a point!
And that you'll be so glad to do,
Because you'll be my POSSLQ.
"A marriage without the marriage" is almost exactly what it is. And it does make sense, not least in legal terms. Things are more complex the closer you look at them.
COHABITANT seems to be another term used in English for "samboer". "Cohabitation, sometimes called consensual union or de facto marriage, refers to unmarried heterosexual couples living together in an intimate relationship." (http://family.jrank.org/pages/279/Cohabitation.html). There are surely different definitions depending on culture and legal system.
In Sweden, if you are not married but have a steady relationship with somone you don't live together with, we can call the partner "SÄRBO", which - however - is not a legally defined relationship, as SAMBO is.
Interesting piece of information: "Cohabitation is a common type of partnership in Norway. Cohabitants have some rights if they have joint children, or if they have lived together for five years. Cohabitants can also regulate their relationship through a cohabitation agreement. In Norway, in 2013, 55.2% of children were born outside of marriage." (https://en.wikipedia.org/wiki/Cohabitation)
You can also be married without living together. Even a marriage can be more complex than it may look like at a first glance. ;-)
Citizenship & Immigration Canada states that a common-law partner refers to a person who is living in a conjugal relationship with another person (opposite or same sex), and has done so continuously for a period of at least one year.
But I like the Norwegian one-word description. :-D
We don't have a proper expression for it, as far as I know. I usually use and hear either "han/hun jeg bor [sammen] med", "roomie" (in informal settings) or jokingly "samboeren".
Example: "Jeg kom hjem etter en lang dag på jobb i går, og så hadde ikke roomien tatt oppvasken engang!" (I came home after a long day at work yesterday, and my roomie hadn't even done the dishes!)
Depending on the setting it can also be "leietakeren" (if you rent out a room in your apartment) or "noen i kollektivet".
In the US, common law husband/wife has a very specific legal definition that doesn't occur in all states and requires a specific length of cohabitation (I've generally heard 7 years, but again, that may vary). I've lived with my partner for almost five years and i wouldn't call him my common law husband. I generally call him my partner, but that still has some connotations of homosexual partnership. US English is just terribly awkward in this regard, even though it's a fairly common relationship arrangement.
That is a common misconception. In the states that still recognize common law marriage, cohabitation alone, regardless of the duration, is never enough to establish a common-law marriage. Generally, the husband and wife have to agree to me married without coercion, be of the legal age to marry, not be already married, live together, and most importantly to hold themselves out to the community as a married couple. The seven-years thing seems to be a complete myth. A few jurisdictions require or required one year of cohabitation to make a valid common-law marriage (in addition to the other requirements). No jurisdiction has ever set seven years as the limit as far as I can tell.
The thing is that 'samboer' is both used both formally (legal term) and informally signalling the fact that you actually live under the same roof as your partner or girl-/boyfriend. The latter is rather the equivalent of 'kjæreste', a word that in itself does not reveal anything about your residential situation. It's probably difficult to find an equivalent in English.
No. I've never seen or heard "sambøren" in use, but I think it would have to mean "the burden that we carry together". (A bør, or byrde, is a burden. The sam prefix means sharing it.)
Slightly similar, but totally unrelated words: samband (comms), samvær (being together, but typically used as custody of a child).