An epithet of the Buddha, used by the Buddha in referring to himself.
The Commentaries (DA.i.59-67; AA.i.58-63; MA.39-43; UdA.128ff., etc.) give eight (sometimes expanded to sixteen) explanations of the word, which shows that there was probably no fixed tradition on the point.
The explanations indicate that the name can be used for any arahant, and not necessarily only for a Buddha.
The term was evidently pre-Buddhistic, though it has not yet been found in any pre-Buddhistic work.