Teen with pint might be sorry (8)
I believe the answer is:
penitent
'sorry' is the definition.
(similar in meaning)
'teen with pint might be' is the wordplay.
'with' means one lot of letters go next to another.
'might be' indicates anagramming the letters.
'teen' put after 'pint' is 'pintteen'.
'pintteen' is an anagram of 'PENITENT'.
(Other definitions for penitent that I've seen before include "Regretting a wrong deed" , "Expressing sorrow for one's sins" , "Showing regret" , "Remorseful" , "Teen pint (anag.)" .)