What is another term for co-worker but for someone ranked higher?

What is a term for a director of a program (or anyone ranked higher) that I don't directly report to, but I've worked with on various committees?

A senior or a senior colleague. As per the Cambridge dictionary definition of senior - high or higher in rank.

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 circles, and it allows for that person to be of a different rank than your own. Associate is a synonym that comes to mind, but I would be wary of using that word. Associate can denote someone of lesser than or equal rank to you, and it could easily be construed as a professional discourtesy.