Sailor's right circling sea's opening deep (8)
I believe the answer is:
abstruse
'deep' is the definition.
(thesaurus)
'sailor's right circling sea's opening' is the wordplay.
'sailor's' becomes 'ab's' (abbreviation for able seaman).
'right' becomes 'true' (associated in meaning).
'circling' indicates putting letters inside (circling can mean going around or containing).
'opening' says to take the initial letters.
The initial letter of 'seas' is 's'.
'true' placed around 's' is 'truse'.
'abs'+'truse'='ABSTRUSE'
(Other definitions for abstruse that I've seen before include "Busts are oddly difficult to understand" , "Hard to understand, recondite" , "Difficult to understand, obscure" , "Hard to understand, complicated" , "Esoteric" .)