Narrow sea channel (6)
'narrow sea channel' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for strait that I've seen before include "Narrow sea-channel" , "Narrow sorts of traits" , "Narrow or difficult" , "of Gibraltar, for example" , "-- -laced (prudish)" .)
(Other definitions for kyle that I've seen before include "Transport system with floating trains" , "Narrow sea channel (in Scotland)" , "- - of Lochalsh" , "Narrow channel (Scots), rhymes with dossier" .)