In the style of a US subject's wake (9)
I believe the answer is:
aftermath
'wake' is the definition.
(synonyms)
'in the style of a us subject's' is the wordplay.
'in the style of' becomes 'after' (I've seen this in another clue).
'a us subject' becomes 'math' (US name for mathematics).
'after'+'math'='AFTERMATH'
(Other definitions for aftermath that I've seen before include "Consequence of an event, situation that follows" , "Situation following as consequence or result" , "Results, often of something bad" , "Consequences of an unpleasant event" , "Subsequent consequence" .)