In dismay, he mentions disorder (6)
I believe the answer is:
mayhem
'disorder' is the definition.
(thesaurus)
'in dismay he mentions' is the wordplay.
'in' indicates a hidden word.
'MAYHEM' is hidden within 'dismay he mentions'.
(Other definitions for mayhem that I've seen before include "Extreme disorder" , "Much trouble when" , "Violent destruction of confusion" , "Big trouble!" , "Violent or damaging action, a crime" .)