Definition of western hemispheres:
(n) :
(US, metonymic) The Americas.
(n) :
The hemisphere in Earth to the west of the Greenwich meridian (zero degree longitude) and east of 180 degrees longitude (approximately the International Date Line), containing the Americas and a small part of eastern Russia.
(n) :
Used other than figuratively or idiomatically: see western, hemisphere.
(n) :
(uncountable) Alternative form of Western Hemisphere. [The hemisphere in Earth to the west of the Greenwich meridian (zero degree longitude) and east of 180 degrees longitude (approximately the International Date Line), containing the Americas and a small part of eastern Russia.]