- A person who shares the role of trustee with one or more people, usually with the same responsibilities and duties. They typically have to cooperate and work together, unless the trust's rules allow independent action
- When the primary trustee was unwell, her brother stepped in as a co-trustee.
- She serves as a co-trustee on her father's trust, alongside her two siblings.
- The co-trustee was required to consult with his counterpart before making any major decisions about the trust's assets.