Definition of fiendishly in US English:

fiendishly

adverb

  • See fiendish

    • ‘At least, it would be if the fiendishly clever designers of the particular variant we had did not have access to the same anti-virus web sites we did.’
    • ‘Word of Nagano got to Frank Zappa, who in 1983 enlisted him to conduct his fiendishly tricky classical works with the London Symphony Orchestra.’
    • ‘It came out very well, though it was fiendishly difficult - the house dates to the 1630s and has very idiosyncratic windows arranged with total lack of symmetry.’
    • ‘This is a fiendishly clever plot, and Burkett is indeed the patsy.’
    • ‘Here's a fiendishly clever game that will keep you engaged until Halloween, or Christmas, depending on how unbusy you are.’

Pronunciation

fiendishly

/ˈfēndiSHlē/