Short railway line (6)
I believe the answer is:
siding
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">short railway line</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for siding that I've seen before include "Short stretch of railway track off the main line" , "Short piece of railway track used for shunting" , "Railway spur" , "Taking one part in an argument on the spare railway track" , "Section of track" .)