Penniless, essentially, having nothing (3)
I believe the answer is:
nil
'nothing' is the definition.
('nil' can be a synonym of 'nothing')
'penniless essentially having' is the wordplay.
'having' says the answer is hidden in the clue.
'NIL' is hidden within 'penniless essentially'.
(Other definitions for nil that I've seen before include "Score of nought" , "Nothing, no score" , "Nothing, zero" , "Nothing, naught" , "Nothing - in Latin" .)