'one endowed with the threefold (higher) knowledge'.
In Brahmanism means 'knower of the 3 Vedas' (tri-vidyā), in Buddhism means one who has realised 3 kinds of knowledge, to wit:
remembrance of former rebirths,
the divine eye,
extinction of all cankers.
For details, s. abhiññā, 4-6. Cf. Tevijjā Sutta, D. 13 (WHEEL 57/58).