Account for one dumped on prairie (7)
I believe the answer is:
explain
'account for' is the definition.
(I've seen this before)
'one dumped on prairie' is the wordplay.
'one dumped' becomes 'ex' (a former partner, someone who was dumped).
'on' says to put letters next to each other.
'prairie' becomes 'plain'.
'ex'+'plain'='EXPLAIN'
(Other definitions for explain that I've seen before include "Show the meaning of, make clear" , "Pin axle (anag.)" , "Interpret" , "Tell us how" , "Justify" .)