monarch (n.)

mid-15c., monark, "supreme governor for life, a sole or autocratic ruler of a state," from Old French monarche (14c., Modern French monarque) and directly from Late Latin monarcha, from Greek monarkhēs "one who rules alone" (see monarchy). "In modern times generally a hereditary sovereign with more or less limited powers" [Century Dictionary, 1897].

As a type of large orange and black North American butterfly by 1885; on one theory it was so called in honor of King William III of England, who also was Prince of Orange, in reference to the butterfly's color. An older name is milkweed-butterfly (1871). Other old names for it were danais and archippus.