Child and adult left equal (5)
I believe the answer is:
total
'equal' is the definition.
(thesaurus)
'child and adult left' is the wordplay.
'child' becomes 'tot' (term for a young child).
'and' says to put letters next to each other.
'adult' becomes 'a' (abbreviation).
'left' becomes 'l' (common abbreviation).
'tot'+'a'+'l'='TOTAL'
(Other definitions for total that I've seen before include "Completely destroy" , "French oil and gas company" , "It might be grand" , "Complete, absolute" , "Damage beyond repair" .)