Something that is affirmed or denied of the subject in a proposition in logic. (Merriam-Webster's Collegiate Dictionary)
In Metacosm: An object evaluating a predicate on a set of Entities before to determine if manipulation on them are allowed. If an Entity manipulation (Action) is guarded by a Predicate, it can only be executed if and only if the guarding Predicate is validated (i.e., it is evaluated as true). A Predicate defines conditions to be verified on a set of Entities. Predicates are implemented as Command (design pattern) objects. As such, they can be serialized and reused in lots of different contexts without needed to be described again.
An inherent characteristic. (Merriam-Webster's Collegiate Dictionary)
In Metacosm: An attribute is a characteristic associated to a Predicate against which the particular aspect of the Predicable tested by this Predicate, is evaluated.
Something that may be predicated. (Merriam-Webster's Collegiate Dictionary)
In Metacosm: An object on which Predicates can operate.
In Metacosm: An object able to manipulate Predicates. In particular, an object able to combine several Predicates into one.