Underground passage (6)
'underground passage' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for subway that I've seen before include "New York city trains" , "American tube" , "New York underground" , "Passage under a road" , "Pedestrian tunnel under a road" .)
'underground passage' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tunnel that I've seen before include "Excavated passage" , "Sight defect" , "(Soppy) fairground ride" , "Passage through or under something" , "Underground passage for road or railway" .)