Widespread piece of disorder, I fear (4)
I believe the answer is:
rife
'widespread' is the definition.
(rife can mean widespread or universal)
'piece of disorder i fear' is the wordplay.
'piece of' indicates a hidden word.
'RIFE' can be found hidden inside 'disorder i fear'.
(Other definitions for rife that I've seen before include "Abounding" , "Of widespread occurrence" , "Widespread like fire" , "is everywhere" , "raging" .)