Devilish

·adj Extreme; excessive.

II. Devilish ·adj Resembling, characteristic of, or pertaining to, the devil; diabolical; wicked in the extreme.

devilish
Very: an epithet which in the English vulgar language is made to agree with every quality or thing; ...

Dictionary of The Vulgar Tongue by Francis Grose
devilish
Atrocious, enormous; excessively, exceedingly. Of the latter or adverbial use of the word Grose says...

Dictionary of American Words And Phrases by John Russell Bartlett.