That feels unnecessarily pedantic. If the sole job of entity X is to perform action Y, and it always performs this action idempotently, then why not describe X as idempotent? It's shorter, and it's clear enough. It might not be precisely accurate in the dictionary definition of the word - but natural languages also have DSLs, and those DSLs evolve to adapt to their use cases. Saying "thing that performs an idempotent action" over and over again is a waste of everybody's time.