What do the following words have in common?

ALLY
REST
ROAD
HEIR
HIGH
RAVEN
ANGER
ALLOW
TROPHY

Each word becomes a new one with the addition of a single letter at the beginning:

RALLY
WREST
BROAD
THEIR
THIGH
CRAVEN
DANGER
CALLOW (F, H, M, S, T, or W)
ATROPHY