Dismissed railway plan (7)
I believe the answer is:
outline
'plan' is the definition.
(outline is a kind of plan)
'dismissed railway' is the wordplay.
'dismissed' becomes 'out' (I've seen this before).
'railway' becomes 'line' (line is a kind of railway).
'out'+'line'='OUTLINE'
(Other definitions for outline that I've seen before include "Possibly tracing" , "Undetailed plan" , "Framework" , "Preliminary draft" , "Sketch, delineate" .)