From Longman Dictionary of Contemporary Englishdastardlydast‧ard‧ly /ˈdæstədli $ -ərd-/ adjective old-fashioned BAD BEHAVIOUR OR ACTIONSvery cruel or evil tales of pirates and their dastardly deeds
Examples from the Corpus
dastardly• This way they reckoned that no news of their dastardly cruelty and cowardice would reach the outside world.• What are the dastardly deeds, thoughts and fantasies which your Negative Ego pokes and taunts you with?• Finally the dastardly renegade arrives, and engages Sister Chiang in conversation.Origin dastardly (1500-1600) dastard “someone without courage, someone evil” ((15-20 centuries)), perhaps from Old Norse dæstr 