Boy hiding in glade (3)
I believe the answer is:
lad
'boy' is the definition.
(informal term for boy)
'hiding in glade' is the wordplay.
'hiding in' means to look at the middle letters.
The middle of 'glade' is 'LAD'.
(Other definitions for lad that I've seen before include "Boy, young man" , "Young fellow" , "Chap, fellow" , "Stable employee" , "Son" .)