The Collaborative International Dictionary of English v.0.48:

Visa \Vi"sa\ (v[=e]"z[.a]), Visa card \Vi"sa card`\ (v[=e]"z[.a]
   k[aum]rd`), prop. n.
   A credit card issued with the Trade Name "Visa" on it; as, he
   charged the dinner to his Visa. Visa is a competitor of
   Master Card, Discover, MBNA, and American Express,
   and other credit card companies.
   [PJC]