A trial, oddly, after profit rises and falls (7)
I believe the answer is:
niagara
'falls' is the definition.
(thesaurus)
'a trial oddly after profit rises' is the wordplay.
'oddly' means one should take alternating letters.
'after' says to put letters next to each other.
'profit' becomes 'gain' ('gain' can be a synonym of 'profit'**).
'rises' says the letters should be written in reverse.
The alternating letters of 'trial' are 'ra'.
'a'+'ra'+'gain'='aragain'
'aragain' backwards is 'NIAGARA'.
'and' is the link.
(Other definitions for niagara that I've seen before include "Waterfall at Iran aga" , "Large water falls" , "River forming part of US-Canada border" , "North American waterfall" , "River linking Lakes Ontario and Erie" .)