BRAIN GAMES VI

The five words below have two things in common. The first does not seem unusual, but it sets these words apart as the second thing -  which is  very unusual. 

FOR
DIG
TEMP
EARN
INTER

HINT:
The same three letters can be added to each word.

Answer:

The letters EST can be added to each word to create new ones:

FOREST
DIGEST
TEMPEST
EARNEST
INTEREST

These words are FALSE SUPERLATIVES. That is, the EST form of the word has nothing to do with the original word.

Credit and reference:
The idea for FALSE SUPERLATIVES came from Will Shortz's puzzle on FALSE COMPARATIVES, published in GAMES - Oct. 1983 under the title BRAIN GAMES. This puzzle is posted in this blog under BRAIN GAMES (IV) - January 29, 2015.