Fussier tailoring producing slit (7)
I believe the answer is:
fissure
'slit' is the definition.
(thesaurus)
'fussier tailoring' is the wordplay.
'tailoring' indicates anagramming the letters.
'fussier' is an anagram of 'FISSURE'.
'producing' is the link.
(Other definitions for fissure that I've seen before include "Cleft" , "Deep crack in rock" , "Long, narrow opening" , "Long, narrow crack" , "Crevice" .)