dastardly

Adjective

 * 1) In the manner of a dastard; marked by cowardice; pusillanimous.
 * 2) Treacherous; given to backstabbing.

Quotations

 * "the unprovoked and dastardly attack by Japan on...December 7th" - Franklin D. Roosevelt in response to the attack on Pearl Harbor (1941)

Adverb

 * 1) In a cowardly or treacherous fashion.