Terrible fire is widespread (4)
I believe the answer is:
rife
'widespread' is the definition.
(rife can mean widespread or universal)
'terrible fire' is the wordplay.
'terrible' indicates an anagram.
'fire' is an anagram of '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" .)