The following names and words can be followed by the same three-letters, in the same order, to form new words.

TEMPE _ _ _
DESI _ _ _
ADO _ _ _
HAT _ _ _
SEA _ _ _
TAPE _ _ _

HINT:
The three letters make up a common word.

Answer:

The letters are RED:

TEMPERED
DESIRED
ADORED
HATRED
SEARED
TAPERED

Credit: LA Times Crossword
Sylvia Bursztyn and Barry Tunick
SCARLET LETTERS (adapted)