office spouse
n. A co-worker with whom one has a very close but nonromantic relationship.
Also Seen As
Another love connection at work? Whoa, says Ms. Hiddema and Mr. Ducoffe. While they may be spending countless hours together and are so close they often communicate without speaking, there is nothing romantic about their relationship, they say.

They're simply office mates who also happen to be soul mates.

Or, to use a term that has come into vogue, Ms. Hiddema and Mr. Ducoffe are office spouses — corporate couples bound by mutual respect, common interests and that particular chemistry of friendship
—Marjo Johne, “Wedded work bliss: the office spouse,” The Globe and Mail, April 05, 2006
Feeling close to your office mate? You're not alone.

As more women find themselves on equal footing with their male counterparts, a new workplace phenomenon is emerging: the office spouse.

A recent study by found that 32 percent of office workers have an "office husband" or "office wife" — that is, a nonromantic relationship — and many have more than one.
—Ieva M. Augstums, “Do you take this co-worker…,” The Dallas Morning News, March 12, 2006
1996 (earliest)
Keith is looking out the window, cradling the telephone in the crook of his neck. "You're the best," he breathes into the mouthpiece in that purr I love. "I'd be lost without you. Okay, see you later." He hangs up the phone and turns … to me.

See, those sweet, soothing words were for Sue, the Other Woman in my husband's life. … Then I remember Sue is his workmate, his pal. He's with the woman I am now comfortable describing as Keith's "office spouse."
—Carla Merolla, “Everything but sex: the office-wife thing,” Cosmopolitan, August 01, 1996