In deep, sailor's steadfast keeping south (8)
I believe the answer is:
abstruse
'in deep' is the definition.
'abstruse' can be an answer for 'deep' (I've seen this in another clue). I am not sure about the 'in' bit.
'sailor's steadfast keeping south' is the wordplay.
'sailor's' becomes 'ab's' (abbreviation for able seaman).
'steadfast' becomes 'true' (I've seen this in another clue).
'keeping' indicates putting letters inside (some letters kept inside).
'south' becomes 's' (abbreviation).
'true' enclosing 's' is 'truse'.
'abs'+'truse'='ABSTRUSE'
Can you help me to learn more?
(Other definitions for abstruse that I've seen before include "Incomprehensible to those with normal understanding" , "Hard to understand, perhaps profound" , "Obscure or recondite" , "Hard to understand, complicated" , "Difficult to understand, obscure" .)