Quote:

And the popular definition varies significantly from its original meaning used among psychologists. See Dale's Wordwizard link. Third post in the thread.



Which says:

From _Brewer's Dictionary of Modern Phrase & Fable_ (2000):
Significant other ... is of American origin, dating from the 1970s, and was adopted from the jargon of sociology as a term for a person who directly influences an individual's self-evaluation and behaviour, as a parent does a child or an employer an employee. [One source says this sociobabble is first recorded in 1940--Susumu]
Feb 14, 2003 Susumu Enomoto, Japan

Interesting: its use in psychology (which I'd thought was its origin) already transforms, narrows, or subverts it; and

Its original meaning would probably not have been "important" other person, but an other giving a significance to someone, that is, in a semiotic sense, to put it briefly, if obtusely.