Windy City trains (3)
I believe the answer is:
els
'windy city trains' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for els that I've seen before include "Angular distances above the horizon" , "Golfer; elevated railways" , "Ernie - - (golfer)" , "South African golfer" , "US urban railways" .)