NPR Weekend Edition Sunday Puzzle
June 18, 2011
Will Shortz

Each of the following words can be changed into a new one by dropping one letter and substituting one of four particular letters for it. What are the new words and what is the significance of the four letters?

ENACT
GAUGE
INSURE
GUEST
CONTEST
PANAMAS
COATING
TWEETER
SUAVER
ELECTION
CONVEY
EMPRESS
PROTECTOR
SUITE
FUNCTION
TENON

Answers: 

The new words are:

EXACT
GAUZE
INJURE
QUEST
CONTEXT
PAJAMAS
COAXING
TWEEZERS
QUAVER
EJECTION
CONVEX
EXPRESS
PROJECTOR
QUITE
JUNCTION
XENON 

The words have been changed by dropping one letter and substituting either J, Q, X, or Z for it. These four letters are the least commonly used letters in the alphabet.