In augmentation, a voice or instrument plays the theme at a slower pace — that is, the note values of the theme are augmented.
An example (in the video below) occurs in the Fugue-Kriti’s Pallavi (Movement I). Here, the veena and solo cello play the fugue subject at half the original tempo.
They are preceded by the violin, which enters 1½ beats earlier with a variation of the subject at the original tempo. This creates a canon — a structure made of staggered, overlapping layers of the same melody.
The combination is referred to as canonic augmentation.

Example: Canonic Augmentation