From WordNet (r) 3.0 (2006) :
USA
n 1: North American republic containing 50 states - 48
conterminous states in North America plus Alaska in
northwest North America and the Hawaiian Islands in the
Pacific Ocean; achieved independence in 1776 [syn: United
States, United States of America, America, the
States, US, U.S., USA, U.S.A.]
2: the army of the United States of America; the agency that
organizes and trains soldiers for land warfare [syn: United
States Army, US Army, U. S. Army, Army, USA]
From V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016) :
USA
United Software Association (org., USA)