Terrible fire is widespread (4)
I believe the answer is:
rife
'widespread' is the definition.
(thesaurus)
'terrible fire' is the wordplay.
'terrible' indicates an anagram.
'fire' with letters rearranged gives 'RIFE'.
'is' is the link.
(Other definitions for rife that I've seen before include "Overabundant" , "Very common or frequently occurring" , "Prevalent" , "Endemic" , "Excessively abundant" .)