Friendly sailor dives in a long way (7)
I believe the answer is:
amiable
'friendly' is the definition.
(similar in meaning)
'sailor dives in a long way' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'dives in' means one lot of letters goes inside another.
'long way' becomes 'mile'.
'a'+'mile'='amile'
'ab' put into 'amile' is 'AMIABLE'.
(Other definitions for amiable that I've seen before include "Charming" , "Of sweet and friendly disposition" , "Good-humoured" , "'Friendly, pleasant and good-tempered (7)'" , "Friendly and good-natured (7)" .)