The following words have something in common. Can you determine what it is?

PRAIRIE
SUNFLOWER
PELICAN
EMPIRE
VOLUNTEER
EVERGREEN

Answer:

They are all official nicknames of U.S. states:

PRAIRE - ILLINOIS
SUNFLOWER - KANSAS
PELICAN - LOUSIANA
EMPIRE - NEW YORK
VOLUNTEER - TENNESSEE
EVERGREEN - WASHINGTON