Learner very exuberant over game (5)
I believe the answer is:
lotto
'game' is the definition.
(the UK National Lottery)
'learner very exuberant over' is the wordplay.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'very exuberant over' becomes 'otto' (I can't justify this - if you can you should give a lot more credence to this answer).
'l'+'otto'='LOTTO'
Can you help me to learn more?
(Other definitions for lotto that I've seen before include "house" , "form of gambling" , "Game like bingo" , "chancy business" , "National gambling game" .)