Yāska (Sanskrit: यास्कः),(6th-5th centuries B.C. accoring to Shukla, Georgetown University) was a Sanskrit grammarian who preceded Pānini. His famous text is Nirukta, which deals with etymology, lexical category and the semantics of words. He is thought to have succeeded Śākaṭāyana, an old grammarian and expositor of the Vedas, who is mentioned in his text. He is sometimes referred to as Yāska ācārya (ācārya = teacher).