| In linguistics, the augment is a vowel prefixed to a verb in some Indo-European languages to make a past tense. The vowel is e- in Greek and Armenian, and a- in Sanskrit. (The change of e to a is a normal phonetic development in Sanskrit.) Greek, Sanskrit, and Armenian form a "central" group within the Indo-European dialects.
The oldest type of verb inflexion is one using the person suffixes -m "I", -s "you", and -t "she, he, it". In the present tense these have a suffix -i, and in the past tense they have the augment prefix e-.
In Sanskrit:
dádâmi 'I give'
dádâsi 'you give'
dádâti 's/he gives'
ádadhâm 'I gave'
ádadhâs 'you gave'
ádadhât 's/he gave'
In Greek:
dídômi 'I give'
dídôs 'you give'
dídôsi 's/he gives'
edídoun 'I gave'
edídous 'you gave'
edídou 's/he gave'
Now there are later phonetic changes obscuring the pattern of endings a bit (loss of final -t in Greek, for one), but this illustrates the original system.
The augment was not always used in the early stages, Homeric Greek and Vedic Sanskrit. In both it was regularized later. So it was probably an independent time particle in Proto-Indo-European.
When the stem began with a vowel (or h), the augment coalesced with it to form a long vowel (the temporal augment): Greek hagiazô 'I hallow', hêgiasa 'I hallowed'. (These verbs use the -ô set of endings, not the older -mi set.)
The perfect was formed by reduplication: luô 'I loose', leluka 'I have loosed'. That is, the consonant of the initial syllable was repeated in an extra syllable. The pluperfect was formed by adding the augment onto the reduplication: eleluka 'I had loosed'.
In Modern Greek the stress on such verbs is on the third-last syllable: ghráfo 'I write' gives éghrapsa 'I wrote'. But in the 1st and 2nd person plural, there is an extra syllable in the ending, and the unstressed augment is dropped: eghrápsame 'we wrote' has become ghrápsame. | 
