What do the following words have in common?

TEN

MALE

BROW

FEIGN 

STAGE

HINT:

The same two letters will change each word into a new one.

Answer:

 

Adding or inserting the letters OR will change each word into a new one:

 

TENOR

MORALE

BORROW

FOREIGN

STORAGE

 

Credit:

Joseph Appel

OR NOT