Kenneth G. Wilson (1923). The Columbia Guide to Standard American English. 1993.
dastard (n.), dastardly (adj.)
A dastard was once a coward, but today the noun is rare and means simply an unprincipled, treacherous villain. The adjective means sneaky, underhanded, and treacherous, and in those meanings still echoes the original sense. Today its a word rather hard to take seriously.