augment

English past tense verbs have -ed as a suffix.  Similarly, Greek verbs showing past time will have an augment.  In most cases, an augment is just an epsilon prefix.  Note the prefix on the aorist forms here:

Imperfect and aorist forms will have an augment.  (BBG 21.10)

There are four ways verbs take an augment:

1. The normal, expected way is if the verb begins with a consonant, then the augment is an epsilon prefix as above.
2. If the verb begins with a single vowel, the augment is formed by lengthening that vowel (α to η, ε to η, ο to ω) so the verb ἀκούομεν would become ἤκουσαμεν.
3. If the verb begins with a dipthong, either the first letter of the dipthong lengthens (ευχαριστεω ηυχαριστουν), or the dipthong is not changed at all (ευρισκω ευρισκον).
4. In compound verbs, the augment will slide in directly between the preposition and the verb (καταλαμβανω to κατελαβεν).

Augments only occur in the indicative (principle 13).

Hebrew:

In KHW, they use the term “unaugmented” or “augmented” in the sense of “unaltered” or “changed”; e.g. the 3ms QTL in the the is unaugmented meaning it has no prefixes or suffixes added to it.