Period before Christmas -- certain son is wanting an exciting experience (9)
I believe the answer is:
adventure
'an exciting experience' is the definition.
(I've seen this before)
'period before christmas certain son is wanting' is the wordplay.
'period before christmas' becomes 'advent' (I've seen this before).
'certain' becomes 'sure' (similar in meaning).
'son' becomes 's'.
'is wanting' suggests deleting specific letters (to want something can mean to lack it or need it).
'sure' with 's' removed is 'ure'.
'advent'+'ure'='ADVENTURE'
(Other definitions for adventure that I've seen before include "Escapade" , "Exciting or dangerous journey" , "Exciting or daring experience" , "Hazardous operation" , "Risky or exciting experience" .)