Awkward ascent on railway line (8)
I believe the answer is:
ancestry
'line' is the definition.
('ancestry' can be a synonym of 'line')
'awkward ascent on railway' is the wordplay.
'awkward' indicates an anagram.
'on' is a charade indicator (letters next to each other).
'railway' becomes 'ry' (abbreviation for railway).
'ascent' is an anagram of 'ancest'.
'ancest'+'ry'='ANCESTRY'
(Other definitions for ancestry that I've seen before include "Line of descendants" , "Blood line" , "Person's ethnic descent" , "race" , "Any crest (anag.)" .)