Threatening tenant from internet café, worryingly (6)
I believe the answer is:
fierce
'threatening' is the definition.
(thesaurus)
'tenant from internet cafe worryingly' is the wordplay.
'from' indicates named letters should be taken away.
'worryingly' indicates anagramming the letters (letters are disturbed or worried).
'internet'+'cafe'='internetcafe'
'internetcafe' with 'tenant' taken out is 'irecfe'.
'irecfe' anagrammed gives 'FIERCE'.
(Other definitions for fierce that I've seen before include "Unpleasantly extreme, not gentle" , "Barbarous" , "Violent in temper or manner" , "intensity" , "Menacingly wild" .)