The augment is an Indo-European verbal prefix used in Indo-Iranian, Greek, Phrygian, Armenian, and Albanian, to indicate past time.[1] The augment might be either a Proto-Indo-European archaic feature lost elsewhere or a common innovation in those languages.[1] In the oldest attested daughter languages, such as Vedic Sanskrit and early Greek, it is used optionally. The same verb forms when used without the augment carry an injunctive sense.[2][3][4]
The augment originally appears to have been a separate word, with the potential meaning of 'there, then', which in time got fused to the verb. The augment is *h₁é- in PIE (é- in Greek, á- in Sanskrit) and always bears the accent.[2][3]