Very mature duke lost in cellar (5)
I believe the answer is:
vault
'very mature duke' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'lost in cellar' is the wordplay.
'lost' becomes 'l' (abbreviation in sporting league tables).
'in' indicates putting letters inside.
'cellar' becomes 'vaut' (I have seen 'old cellar' mean 'vaut' so perhaps 'cellar' could also mean 'vaut').
'l' put within 'vaut' is 'VAULT'.
Can you help me to learn more?
(Other definitions for vault that I've seen before include "Leap - arched ceiling" , "Underground chamber - leap" , "Leap; storage chamber" , "Bank's strongroom" , "Burial chamber - jump across" .)