Answer:

hub

Answer	Crossword Clue
HUB	Axle end
HUB	Focal point
HUB	Boston

HUB	Boston nickname
HUB	Boston sobriquet
HUB	Where radii meet
HUB	Center
HUB	Axle attachment
HUB	Boston moniker
HUB	Airline's main airport
HUB	Flight-connection site

HUB	Where spokes meet
HUB	Busy airport
HUB	Wheel part
HUB	Focus of activity
HUB	Atlanta, for Delta Airlines
HUB	Center of activity
HUB	O'Hare, for United Airlines
HUB	Air base?

HUB	LAX or JFK, for American Airlines
HUB	US Airways has one in Phoenix
HUB	Where the action is
HUB	Center of operations, to an airline
HUB	Spokes' center
HUB	Boston, with "the"
HUB	O'Hare, for one
HUB	Wheel's center

HUB	Major airport
HUB	Core
HUB	Destination for a Trivial Pursuit winner
HUB	Nexus
HUB	Where planes are often changed
HUB	Airline locale
HUB	Nerve center
HUB	Boston's nickname

HUB	Connecting flight site
HUB	Where some routes meet
HUB	Airport with many connecting flights
HUB	Wheel center
HUB	Bub or cap opener