Man, say, is somewhat travel-sick heading north (4)
I believe the answer is:
isle
'man say' is the definition.
(Isle of Man)
'somewhat travel-sick heading north' is the wordplay.
'somewhat' says the answer is hidden in the clue.
'heading north' says the letters should be written in reverse (in a down clue, letters travel north).
'elsi' can be found hidden inside 'travel sick'.
'elsi' backwards is 'ISLE'.
'is' is the link.
(Other definitions for isle that I've seen before include "cut-off location" , "-- of Dogs, area of London" , "eg Man, Dogs" , "Dogs, for example" , "Small area of land in water" .)