means A single ruler—a king, queen, or emperor—who holds sovereign power over a state, usually for life and often by inheritance.

from From Greek 'monarkhes,' a tidy compound of 'monos' (alone, single) and 'arkhein' (to rule)—literally 'one who rules alone.' It traveled through Latin 'monarcha' and Old French before settling into English. That same 'arkhein' fathers a whole dynasty of words: 'anarchy' (no ruler), 'oligarchy' (rule by a few), 'hierarchy' (sacred rule). The butterfly, incidentally, got the name much later—possibly an 18th-century nod to its regal orange-and-black coloring, fit for a king.