Probably the name of a brahmin clan, the Agnivesyāyanas, and the Ksatriyas who were so styled, took the name from their brahmin priests.
The name is used by the Buddha in addressing Saccaka Nigaṇṭhaputta, MN.i.229f. MN.i.237f. and also Dīghanakha Paribbājaka. MN.i.497f.
In the Dantabhūmi Sutta MN.iii.128f. the novice Aciravata is thus addressed by Prince Jayasena, who visits him, and also by the Buddha.