Endlessly humble wiseacre (3)
I believe the answer is:
owl
'wiseacre' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'endlessly humble' is the wordplay.
'endlessly' says to take the centre (the ends of the words are removed).
'humble' becomes 'lowly' (synonyms).
The central letters of 'lowly' are 'OWL'.
Can you help me to learn more?
(Other definitions for owl that I've seen before include "Low kind of wise bird" , "Athena's bird" , "eg Snowy, Tawny" , "Someone solemn or wise or staying up at night" , "Winged hooter" .)