A trait is a part of the definition of an entity.
That's right.
A policy is applied to an entity to modify a trait or traits of the entity.
I think in this case mixure of terms is only misleading. What trait does checking policy modify CheckingPolicy in SmartPointer? I would just say: "A policy is applied to an entity to modify it". It could modify it's defintion, behavior, both, e.t.c.
Shorter Oxford English Dictionary (abbreviated) " Policy
5. A course of action adopted and pursued by a government, party, ruler or statesman, etc; any course of action adopted as advantageous or expedient. (The chief living sense). (Late midle english).
This looks like most close.
Trait
4. A distinguishing quality; a characteristic 1752.
This looks like most close.
regards
Andy Little
Gennadiy