An augment is a vowel (usually e) added (augmented) to the beginning of a verb. The augment indicates that the verb is in the past tense. This only occurs if the mood of the verb is the Indicative.

English does something similar to the indicative mood in the past tense; it usually adds the letters "ed" to the end (rather than to the beginning of a word as Greek does with the augment). The effect is the same.

1. Add "e" if the verb begins with a consonant
2. Lengthen (augment) the initial vowel if a verb begins with a vowel.