Shelled facility is twisted and sloping (6)
I believe the answer is:
italic
'sloping' is the definition.
(I've seen this before)
'shelled facility is twisted' is the wordplay.
'shelled' says to take the centre (the outer letters or shell are removed).
'is twisted' indicates an anagram.
The central letters of 'facility' are 'acilit'.
'acilit' anagrammed gives 'ITALIC'.
'and' is the link.
(Other definitions for italic that I've seen before include "Sloping font" , "Printed in a sloping type" , "Relating to slanting handwriting or type" , "from Rome?" , "Type of script" .)