Shoe: edge held by boy (4-2)
I believe the answer is:
slip-on
'shoe' is the definition.
(I know that slip-on is a type of shoe)
'edge held by boy' is the wordplay.
'edge' becomes 'lip' (lip is a kind of edge).
'held by' is an insertion indicator.
'boy' becomes 'Son' (synonyms).
'lip' going inside 'son' is 'SLIP-ON'.
(Other definitions for slip-on that I've seen before include "Shoe without laces" , "Not a lace-up" , "Shoe without fasteners" , "Garment or shoe with little or no fastening" , "Shoe, not a 10" .)