The Collaborative International Dictionary of English v.0.48:

Ethos \E"thos\, n. [L., fr. Gr. ? character. See Ethic.]
   1. The character, sentiment, or disposition of a community or
      people, considered as a natural endowment; the spirit
      which actuates manners and customs; also, the
      characteristic tone or genius of an institution or social
      organization.
      [Webster 1913 Suppl.]

   2. (esthetics) The traits in a work of art which express the
      ideal or typic character -- character as influenced by the
      ethos (sense 1) of a people -- rather than realistic or
      emotional situations or individual character in a narrow
      sense; -- opposed to pathos.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

ethos
    n 1: (anthropology) the distinctive spirit of a culture or an
         era; "the Greek ethos"