To resolve tiffs can be difficult (5)
I believe the answer is:
stiff
'difficult' is the definition.
(I've seen this before)
'to resolve tiffs' is the wordplay.
'to resolve' indicates anagramming the letters (I've seen 'resolved' mean this).
'tiffs' with letters rearranged gives 'STIFF'.
'can be' is the link.
(Other definitions for stiff that I've seen before include "One dead" , "Difficult" , "Awkward" , "Formal" , "Frigid" .)