Amount held by penniless!? (3)
I believe the answer is:
nil
'amount' is the definition.
(nil is a kind of amount)
'held by penniless?' is the wordplay.
'held by' says the answer is hidden in the clue.
'NIL' is hidden in the letters of 'penniless'.
(Other definitions for nil that I've seen before include "Nothing, no score" , "Nothing, naught" , "none" , "Score of nought" , "Nothing found in senility" .)