The Collaborative International Dictionary of English v.0.48:

Archangel \Arch`an"gel\, n. [L. archangelus, Gr. 'archa`ggelos:
   cf. OF. archangel, F. archange. See Arch-, pref., and
   Angel.]
   1. A chief angel; one high in the celestial hierarchy.
      --Milton.
      [1913 Webster]

   2. (Bot.) A term applied to several different species of
      plants (Angelica archangelica, Lamium album, etc.).
      [1913 Webster]

WordNet (r) 3.0 (2006):

archangel
    n 1: an angel ranked above the highest rank in the celestial
         hierarchy
    2: a biennial cultivated herb; its stems are candied and eaten
       and its roots are used medicinally [syn: garden angelica,
       archangel, Angelica Archangelica]