It heartens seafarers a great deal (3)
I believe the answer is:
far
'a great deal' is the definition.
Both the definition and answer are adverbs. Perhaps there's a link between them I don't understand?
'it heartens seafarers' is the wordplay.
'FAR' is hidden in amongst the letters.
But, I'm unsure how this is indicated.
Can you help me to learn more?
(Other definitions for far that I've seen before include "Distant" , "Very much" , "A long, long way to go" , "Remote" , "At a great distance way" .)