The affix itra comes after the verb pū 'to purify' with the sense of the agent so expressed being the instrument when the sense of the complete word is simply appellative and not descriptive.,
The verb पू includes two verbs पूङ् and पूञ् both meaning 'to purify', but belonging to two different conjugations; as पवित्रं an instrument for cleansing or purifying, such as a sieve or a strainer; and in this sense it means 'two blades of Kusa grass used at sacrifices in purifying and sprinkling ghee'. It also means 'the sacred thread, the clarified butter, &c'.,