What is the role of the word "protected" in the following sentence?
She kept her money protected in a safe.
I mean, she is the sub., kept is the v. and ... so what about the word "protected"?
The word protected is an adjective used as an object complement or predicative complement. It is the past participle of the verb protect, used as an adjective, and it describes the result of keeping.
In grammar, an object complement is a predicative expression that follows a direct object of an attributive ditransitive verb or resultative verb and that complements the direct object of the sentence by describing it.1[3] Object complements are constituents of the predicate. Noun phrases and adjective phrases most frequently function as object complements.[4]
The verb in the sentence kept is complex-transitive, in that it has a direct object money and the object complement protected. This link has multiple similar examples:
In English grammar, a complex transitive is a verb that requires both a direct object and another object or an object complement.