Not easy to grasp by sailors on land (8)
I believe the answer is:
abstract
'not easy to grasp' is the definition.
I can't tell whether this definition defines the answer.
'sailors on land' is the wordplay.
'sailors' becomes 'abs' (AB is short for able seaman).
'on' means one lot of letters go next to another.
'land' becomes 'tract' (I've seen this in other clues).
'abs'+'tract'='ABSTRACT'
'by' acts as a link.
Can you help me to learn more?
(Other definitions for abstract that I've seen before include "Extract; summary" , "Appropriate - theoretical - summary" , "Theoretical; abstruse" , "Brats act in non-concrete way" , "Conceptual" .)