Sweet son entering wasteland (7)
I believe the answer is:
dessert
'sweet' is the definition.
(I know that sweet can be written as dessert)
'son entering wasteland' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'entering' indicates putting letters inside.
'wasteland' becomes 'desert' (I've seen this before).
's' going into 'desert' is 'DESSERT'.
(Other definitions for dessert that I've seen before include "Spotted Dick is one" , "Christmas pudding maybe" , "Pudding, sweet" , "Fool possibly" , "Charlotte maybe" .)