There’s a word or two missing from the English language

In my personal life, I have acquaintances, I have friends, and I have good/close friends.

In my work life, I have colleagues – the professional equivalent of acquaintances.

But what comes after that professionally?  We spend over half our waking life at work.  Of course we are going to build important relationships.  Some of them will cross over to personal and become legitimate “friends” or “good friends.” I always feel some sense of honor when a colleague introduces me to someone as a true friend.

But for those that don’t cross that chasm – for those who are truly just professional relationships but ones with increasing closeness – what are we supposed to call them?

I guess in a pinch we could call the next level up “work friends,” although that sounds odd and a bit impersonal.  But what about the level after that?  What is a “work good friend” or even a “good work friend”?  Those sound even weirder.  And yet, “work good friends” abound!  I can probably think of 5 or 10 “work friends” or “work good friends” for every true friend or good friend in the workplace.

Has anyone found a good word or phrase for this yet?