In linguistics, an agent noun (or nomen agentis) is a word that is derived from another word denoting an action, and that identifies an entity that does that action. For example, "driver" is an agent noun formed from the verb "drive". The endings "-er", "-or", and "-ist" are commonly used in English to form agent nouns. "Agent noun" is also used as the name of the derivational meaning (also called a derivateme).
Usually, derived in the above definition has the strict sense attached to it in morphology, that is the derivation takes as an input a lexeme (an abstract unit of morphological analysis) and produces a new lexeme. However, the classification of morphemes into derivational morphemes and inflectional ones is not generally a straightforward theoretical question, and different authors can make different decisions as to the general theoretical principles of the classification as well as to the actual classification of morphemes presented in a grammar of some language (for example, of the agent noun-forming morpheme).
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