Smoke: I react and get poorly (9)
I believe the answer is:
cigarette
'smoke' is the definition.
(I've seen this before)
'i react and get poorly' is the wordplay.
'and' says to put letters next to each other.
'poorly' indicates an anagram.
'i'+'react'='ireact'
'ireact' put after 'get' is 'getireact'.
'getireact' is an anagram of 'CIGARETTE'.
(Other definitions for cigarette that I've seen before include "Tobacco wrapped in paper" , "Something smoked" , "Fag, coffin nail" , "Fag, smoke" , "harmful in nature" .)