A man or woman in the workplace with whom one shares a special relationship having bonds similar to those of a marriage: special confidences, loyalties, shared jokes and experiences, and unusual degree of honesty or openness
Your workmates are the people you work with. My workmates, and, even more, the management, didn't want me to leave. = colleague. someone you work with = colleague
[ 'w&rk ] (noun.) before 12th century. Middle English werk, work, from Old English werc, weorc; akin to Old High German werc work, Greek ergon, Avestan varandzem activity.