Poor national charity gets to moan (6)
I believe the answer is:
lament
'to moan' is the definition.
(thesaurus)
'poor national charity' is the wordplay.
'poor' becomes 'lame'.
'national charity' becomes 'nt' (abbreviation for National Trust).
'lame'+'nt'='LAMENT'
'gets' acts as a link.
(Other definitions for lament that I've seen before include "complaint" , "Express grief" , "Bemoan, bewail" , "Mourn (a person's death)" , "Dirge; bewail" .)