English sit and carp about having to rehearse (8)
I believe the answer is:
practise
'to rehearse' is the definition.
(synonyms)
'english sit and carp about' is the wordplay.
'english' becomes 'e' (abbreviation).
'and' is a charade indicator (letters next to each other).
'about' is a reversal indicator.
'e'+'sit'+'carp'='esitcarp'
'esitcarp' in reverse letter order is 'PRACTISE'.
'having' is the link.
(Other definitions for practise that I've seen before include "Be engaged in (profession)" , "Contrive by some means" , "Rehearse" , "Custom" , "Observe" .)