A little upset, altruism lacking in charity (4)
I believe the answer is:
alms
'charity' is the definition.
(alms is a kind of charity)
'a little upset altruism lacking' is the wordplay.
'upset' says the letters should be written backwards.
'a little' says the answer is hidden in the clue (a little bit of the clue).
'smla' is hidden within 'altruism lacking'.
'smla' reversed gives 'ALMS'.
'in' is the link.
(Other definitions for alms that I've seen before include "handed over as charity" , "Charitable donations to the needy" , "Relief for the poor" , "Charity for poor" , "Charitable aid to poor" .)