In somebody’s trust
Definition 1 of 1
Pro Tip 1/3Emotional Weight
Conveys a sense of honor and seriousness, as it implies a special bond of fidelity. 
He held the family heirloom in his grandmother's trust.
Pro Tip 2/3Entrusted Responsibility
Suggests a task or role given because of a belief in one’s integrity or abilities. 
The museum artifacts were placed in the curator's trust.
Pro Tip 3/3Relationship Depth
Use it to indicate a deep level of trust built over time, not casual relationships. 
As her mentor, I was in her trust to guide her career decisions.