Various ancestors display application (6)
I believe the answer is:
usance
'application' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'various ancestors display' is the wordplay.
'display' says the answer is hidden in the clue (I've seen 'displaying' mean this).
'USANCE' is hidden in the letters of 'various ancestors'.
Can you help me to learn more?
(Other definitions for usance that I've seen before include "period of reckoning" , "interest in redemption" , "old custom" , "Usage (archaic)" , "Time allowed to pay" .)