Higher land might be cold without a coat (4)
I believe the answer is:
hill
'higher land' is the definition.
'hill' can be an answer for 'land' (I have seen 'High land ' mean 'hill' so perhaps 'land' could also mean 'hill'). I'm not certain of the 'higher' bit.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for hill that I've seen before include "Canvasser of opinions" , "Incline" , "High point, but not a mountain" , "Gradient" , "Mount" .)