Seasonal visitor, hill-dweller in South Africa (5)
I believe the answer is:
santa
'seasonal visitor' is the definition.
'hill-dweller in south africa' is the wordplay.
'hill-dweller' becomes 'ant' (I've seen this before).
'in' indicates putting letters inside.
'south africa' becomes 'sa' (abbreviation).
'ant' put into 'sa' is 'SANTA'.
(Other definitions for santa that I've seen before include "Saint Nicholas" , "visitor bringing gifts" , "Dad in a red and white outfit?" , "Present bringer" , "Children's name for Mr Claus" .)