The Collaborative International Dictionary of English v.0.48:

Viceroy \Vice"roy\, n. [F. vice-roi; pref. vice- in the place of
   (L. vice) + roi a king, L. rex. See Vice, prep. and Royal.]
   1. The governor of a country or province who rules in the
      name of the sovereign with regal authority, as the king's
      substitute; as, the viceroy of India.
      [1913 Webster]

   2. (Zool.) A large and handsome American butterfly
      (Basilarchia archippus syn. Limenitis archippus). Its
      wings are orange-red, with black lines along the nervures
      and a row of white spots along the outer margins. The
      larvae feed on willow, poplar, and apple trees.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Limenitis archippus
    n 1: showy American butterfly resembling the monarch but smaller
         [syn: viceroy, Limenitis archippus]