The most accurate word choice, given your explained relationship, is colleague. The Merriam-Webster Dictionary defines colleague. An associate or coworker typically in a profession or in a civil or ecclesiastical office and often of similar rank or state A fellow worker or professional Therefore, colleague is appropriate as it may be used to describe nearly everyone within your professional ...
In a social setting, it would probably be OK to refer to them as your colleague. However, if they are much senior to you it would probably be more polite to say "Mr X is a head of department at the firm where I work," or whatever is appropriate.
Colleague implies same level or type of job In contrast to other answers that describe colleague as more general (because it applies also to similar positions in other companies), I perceive that there's a different aspect where co-worker is more general. Namely, different levels or types of jobs - if you're working as, say, a designer in company, then the company's CFO and janitor are your co ...
Is there a word for "more experienced colleague?" In particular, they have the same rank, but more experience on the job. Edit: Thanks for the answers! I was wondering, is there a word like
1 You might consider cohort: An assistant, colleague, accomplice. or A company, band; esp. of persons united in defence of a common cause. If you wanted a word that expresses solidarity as students, this might be a good choice.
Excluding the last possibility, colleague and business partner are therefore synonymous in their working together in various ways. Some definitions of business seem restricted to commercial activity.