The Collaborative International Dictionary of English v.0.48:

Monarch \Mon"arch\, n. [F. monarque, L. monarcha, fr. Gr. ?, ?;
   mo`nos alone + ? to be first, rule, govern. See Archi-.]
   1. A sole or supreme ruler; a sovereign; the highest ruler;
      an emperor, king, queen, prince, or chief.
      [1913 Webster]

            He who reigns
            Monarch in heaven, . . . upheld by old repute.
                                                  --Milton.
      [1913 Webster]

   2. One superior to all others of the same kind; as, an oak is
      called the monarch of the forest.
      [1913 Webster]

   3. A patron deity or presiding genius.
      [1913 Webster]

            Come, thou, monarch of the vine,
            Plumpy Bacchus.                       --Shak.
      [1913 Webster]

   4. (Zool.) A very large red and black butterfly (Danais
      Plexippus); -- called also milkweed butterfly and
      monarch butterfly.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Monarch \Mon"arch\, a.
   Superior to others; preeminent; supreme; ruling. "Monarch
   savage." --Pope.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

monarch butterfly \mon"arch but"ter*fly\, n. (Zool.)
   A very large red and black butterfly (Danais Plexippus)
   having striking orange-brown wings with black veins in a
   reticulated pattern; -- called also milkweed butterfly and
   monarch. Its larvae feed on the leaves of the milkweed.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

monarch
    n 1: a nation's ruler or head of state usually by hereditary
         right [syn: sovereign, crowned head, monarch]
    2: large migratory American butterfly having deep orange wings
       with black and white markings; the larvae feed on milkweed
       [syn: monarch, monarch butterfly, milkweed butterfly,
       Danaus plexippus]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "monarch":
   anointed king, boss, chief, chieftain, crowned head, czar, dynast,
   emperor, empress, grand duke, high chief, imperator, king,
   king-emperor, kinglet, lord, lord paramount, majesty, master,
   overlord, owner, paramount, petty king, potentate, prince,
   prince consort, queen, royal, royal personage, royalty, ruler,
   sovereign, suzerain, tetrarch



The Devil's Dictionary (1881-1906):

MONARCH, n.  A person engaged in reigning.  Formerly the monarch
ruled, as the derivation of the word attests, and as many subjects
have had occasion to learn.  In Russia and the Orient the monarch has
still a considerable influence in public affairs and in the
disposition of the human head, but in western Europe political
administration is mostly entrusted to his ministers, he being
somewhat preoccupied with reflections relating to the status of his
own head.