Sociology. the fundamental character or spirit of a culture; the underlying sentiment that informs the beliefs, customs, or practices of a group or society; dominant assumptions of a people or period: In the Greek ethos the individual was highly valued.
the character or disposition of a community, group, person, etc.
the moral element in dramatic literature that determines a character's action rather than his or her thought or emotion.
These stories and countless others attest to the democratic ethos of social mobility and fluidity, heavily inflected by the Romantic ethos of "rugged individualism" and, however reductivist, Emersonian "self-reliance."
-- Ann Lauterbach, The Night Sky: Writings on the Poetics of Experience, 2005
Irony is not dead--it's (ahem) a useful rhetorical tool--but it's certainly not the ethos of our age.
-- Jonathan D. Fitzgerald, "Sincerity, Not Irony, Is Our Age's Ethos," The Atlantic, Nov. 20, 2012
Ethos comes from the Greek term meaning "custom; habit; character," and provides the root for the term ethics. It entered English in the 1600s.