Definition of dastardly in US English:

dastardly

adjective

dated, humorous
  • Wicked and cruel.

    ‘pirates and their dastardly deeds’
    • ‘The dastardly villains are the ones in the red uniforms who speak as if they've just swallowed a plum.’
    • ‘The debt recovery agency that carried out the dastardly deed is not expected to have its contract renewed.’
    • ‘She goes undercover at the Miss United States Pageant in Texas to foil the dastardly deeds of an urban terrorist, who plans to blow the event to bits.’
    • ‘Can they be so dastardly and despicable as to attack the president during a presidential campaign?’
    • ‘It is a classic tale of good and evil with an orphan hero, a plucky girl to befriend him, dastardly villains, a bit of a twist and an element of magic.’
    • ‘Have you ever wondered why these evil and dastardly beings might be interested in us?’
    evil, sinful, immoral, wrong, morally wrong, wrongful, bad, iniquitous, corrupt, black-hearted, ungodly, unholy, irreligious, unrighteous, sacrilegious, profane, blasphemous, impious, base, mean, vile
    wicked, evil, iniquitous, heinous, villainous, diabolical, diabolic, fiendish, vicious, murderous, barbarous, cruel, black, dark, rotten, nefarious, vile, foul, monstrous, shocking, outrageous, atrocious, abominable, reprehensible, despicable, execrable, corrupt, degenerate, reprobate, sordid, depraved, dissolute, bad, base, mean, low, dishonourable, dishonest, unscrupulous, unprincipled, underhand, roguish
    View synonyms

Origin

Mid 16th century (in the sense ‘dull or stupid’): from dastard in the obsolete sense ‘base coward’.

Pronunciation

dastardly

/ˈdastərdlē//ˈdæstərdli/