Pirates' town drops a letter as expression of regret (7)
I believe the answer is:
penance
'regret' is the definition.
(I know that penance is a type of remorse)
'pirates' town drops a letter as expression' is the wordplay.
I cannot quite see how this works, but
'a' could be 'an' and 'an' is found within the answer.
'letter' could be 'pe' (pe is a kind of letter) and 'pe' is present in the answer.
This explanation may well be incorrect...
'of' acts as a link.
Can you help me to learn more?
(Other definitions for penance that I've seen before include "Punishment imposed for sin" , "sacrament" , "Punishment for wrongdoing, by religion perhaps" , "Mortification" , "Expression of sorrow for sin" .)