Sailor's patch of land is speculative (8)
I believe the answer is:
abstract
'speculative' is the definition.
(thesaurus)
'sailor's patch of land' is the wordplay.
'sailor's' becomes 'ab's' (abbreviation for able seaman).
'patch of land' becomes 'tract' (I can't explain this - if you can you should give a lot more credence to this answer).
'abs'+'tract'='ABSTRACT'
'is' is the link.
Can you help me to learn more?
(Other definitions for abstract that I've seen before include "Take away - theoretical" , "Rothko work?" , "Half-inch" , "Remove; theoretical" , "Theoretical; abstruse" .)