What do the following words have in common?

IN
UP
AX
ZEN
PIER
WARD
ACHES
MEDIAN

HINT;
Each word can be preceded by the same two letters.

Answer:

Each word can be preceded by CO to create a new word:

COIN
COUP
COAX
COZEN
COPIER
COWARD
COACHES
COMEDIAN 

NOTE: This puzzle was published in the October, 2014 issue of GAMES - WORLD OF PUZZLES  Magazine under the title of IN GOOD COMPANY.