What do the following words have in common?

ARTS

EASY

ALMS

SEAL

ARK

BASE
AVER

HINT:

The same two letters can either precede or be inserted into each clue to create new words.

Answer:

The letters QU will change each clue into a new word:

QUARTS

QUEASY

QUALMS

SQUEAL

QUARK

BASQUE
QUAVER 

Credit: NY Times Crossword - Nov. 7, 1999
Brendan Emmett Quigley
CUES