Sailor meaning a great deal to his friend (7)
I believe the answer is:
matelot
'sailor' is the definition.
(I've seen this before)
'a great deal to his friend' is the wordplay.
'a great deal' becomes 'lot' (both can mean a large amount).
'to' says to put letters next to each other (I've seen this in other clues).
'his friend' becomes 'mate' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'lot' after 'mate' is 'MATELOT'.
'meaning' is the link.
Can you help me to learn more?
(Other definitions for matelot that I've seen before include "A lot met (anag) - sailor" , "One sailor" , "One at sea" , "Sailor (slang from French)" , "seafarer" .)