A vowel prefixed, or a lengthening of the initial vowel, to mark past time, as in Greek and Sanskrit verbs.
In linguistics, the augment is a syllable added to the beginning of the word in certain Indo-European languages, most notably Greek (the augment survives and has been generalised in Modern Greek), Armenian, and the Indo-Iranian languages such as Sanskrit, to form the perfect, preterite, or aorist tenses.