What do all of the words below have in common?

SO             BUS
TO             ALL
AN            MAN
THE          WAR
LAD          DEN

HINT:
They can all be changed into new words in the same way.

Answer:

Each word becomes a new one when Y is added at the end. 

Credit: 
GAMES/World of Puzzles
May, 2018
Scott Erdman
WORDS TO THE WISE