The Etymology of "Buddha"

Proto-Indo-European (PIE) reconstructed root for "to be awake" "to be aware".

Remove the 'e' to form the zero-grade of the verbal root.

'E' removed.

PIE had the verbal adjective *-tó- which could be added to the zero-grade of the verbal root. This denoted a completed action and is semantically akin to English past participles.

This produces something like: "the awakened one" or by extension, "the enlightened one".

Next, *-tó- dissimilates to *-dó-. Leaving us with...

Indo-Iranian merges *e and *o as *a

Almost there! Next, we apply "Grassmann's Law", named for Hermann Grassmann, who discovered it. This happened in Ancient Greek and Sanskrit. Here, we're concerned with Sanskrit.

Grassmann's Law states: "If an aspirated consonant is followed by another aspirated consonant in the next syllable, the first one loses the aspiration."