from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Intransitive and having an experiencer as its subject, that is, the (syntactic) subject is not a (semantic) agent.
- n. An unaccusative verb.
un- + accusative, from the fact that in a nominative-accusative language, the accusative case, which marks the direct object of a transitive verb, typically marks the non-volitional role. In unaccusative verbs, the non-volitional arguments do not take the accusative case. (Wiktionary)