Seek to provide the railway with a junction (3)
I believe the answer is:
try
'seek' is the definition.
(I know that seek can be written as try)
'the railway with a junction' is the wordplay.
'the railway' becomes 'ry' (abbreviation).
'with' says to put letters next to each other.
'a junction' becomes 't'.
'ry' put after 't' is 'TRY'.
'to provide' acts as a link.
(Other definitions for try that I've seen before include "A rugby score, result of effort" , "Attempt - hear (legally)" , "crack" , "Four rugby points" , "Examine" .)