What unusual property do these words share?

RESTORES

INGRATIATING

TORMENTOR

IONIZATION

ENTERTAINMENT

REDISCOVERED
MICROCOSMIC
BLEACHABLE
ENTITLEMENT

HINT #1: EINSTEIN and UNDERGROUND could be added to the list.

HINT #2: It has to do with letters.

Answer:

Each of these words begins and ends with the same three letters.