The question came from Lynne Murphy via Twitter: “Have you been hearing any ‘sectioned’ in US?”
Me: “No. What’s it mean?”
Her: “Committed, in the ‘institutionalized’ sense.”
The reason she asked was that one of her Twitter informants, who goes by the handle @ahab99, had heard the word coming out of the mouth of American characters on the American-set Netflix series “Mindhunter.” And sure enough, in Episode One, the wife of a hostage-taker says, “I tried to get him sectioned on Sunday” An FBI agent, apparently hard of hearing, follows up, “You tried to get him sectioned?”
The OED definition of the verb is, “To cause (a person) to be compulsorily detained in a psychiatric hospital in accordance with the provisions of the relevant section of the Mental Health Act of 1983 or (formerly) that of 1959.” All the citations are from British sources, including the first one, from a 1984 article in a medical journal: “Before the 1983 Act came into being no social worker ever refused my request to come and see a patient with a view to sectioning the patient under the old section 29.”
I would venture to say that, until now, the word has never been used in an American context.
And how did “sectioned” get into “Mindhunter”? The answer turns out to be simple. The writer of the episode, Joe Penhall, was raised in Australia but has done all his previous work in British theater and film.
That’s all well and good, but it’s pretty odd, as @ahab99 observed, that “apparently nobody in production or on set said ‘wait, what’s “sectioned”?’”
notoneoffbritishisms.com 
Folks on-set may have assumed that it was standard FBI jargon. Actors are often asked to say things they don’t understand, and deliver them as if they did.
While all the comments below are interesting, this one is probably the most accurate.
I remember many years ago Anthony Edwards on a talk show claiming that just off-camera the set of ER was full of Post-It notes reminding them of what various medical jargon terms meant. He (in a friendly tone and probably half-jokingly) singled out George Clooney as particularly reliant on them.
My brother works in mental health in Australia. The word is used by professionals in that field, but I’ve never heard it in general conversation.
that surprises me, since everyone I know knows what Section 8 is in the US, the mandatory hospital stay for possibly dangerous behavior. Maybe that’s because I have a couple of people with bipolar disorder in the family, but being “sectioned” seems rather common.
That’s not what Section 8 is.
oh yeah. What was I thinking. I’m thinking about 5150. Thanks Adam.
Forgot to say that I live in No. Calif.
I remember Corporal Klinger in M*A*S*H (1972-83) trying to ‘get a section 8’ by dressing up as a woman.
In the UK the phrase we commonly hear on the news is “x has been sectioned under the mental health act.”
I am interested to know whether this usage derived from contracting ‘section of an act of parliament/congress’ into a verb or from the dictionary definition ‘section (noun) a distinct group within a larger body of people or things’ – i.e. isolated from society – being ‘verbed’.
I’ve never heard Section 8 – I’d need that explained to me if I heard someone say it. But if someone told me they had someone “committed” – that, I would understand. (AmE, Midatlantic, older millennial)
Payback for all those times I’ve seen British characters in US shows giving distances in blocks.
My wife and I recently watched a program about Mt. Rushmore and the expression “Sent telegrams, usually collect,” was used. My wife asked what that meant. I explained. In the U.K. we get used to car parts spelled and named differently on American films, TV etc. I can’t see it as a problem. You ask, you get an answer, you learn.
I have no problem with Americanisms, I’ve been read American books since my teens and watching American TV and visiting America.
The problem is, when an English character in Person of Interest, for instance, in a scene set in London, tells another character (not an American) that there’s a hospital X blocks away, my first thought is that character can’t be English. My second thought is that whoever wrote that line can’t have looked at a street map of London.
Yeah, “section 8” is known from M*A*S*H and other pop culture sources associated with US Military culture. Is it mentioned by name in Catch-22? Psychiatric discharge is certainly a plot element in that novel, but I don’t recall whether the term “section 8” is used.
But the verb “to section” in that sense, and the participle form “sectioned”, I’ve never heard in US usage. “Committed” would be the American equivalent.
The only time hear Section 8 in the US is in connection with public housing. The mental health connotation is specifically military, so wouldn’t apply to actions the FBI might try to take against a civilian.
Section 8 was a category of discharge from the United States military, used for a service member judged mentally unfit for service. The term comes from Section VIII of the World War II-era United States Army Regulation 615-360, which provided for the discharge of those deemed unfit for military service. It covered a variety of circumstances.
This is clip illustrates the term pretty well. CONTAINS MILD OBSCENITY.