Social-colleague
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A person who is not quite a friend yet but more than an acquaintance. You take part in [light-hearted] chat and would [most probably] only talk to them if you were with a group of people; the same goes for hanging out with them. You also might say Hi to them when meeting in the street, but you wouldnt [stop and chat].
Social-colleague meaning & definition 1 of Social-colleague.