British sailors possessing deficiency, still getting stick (10)
I believe the answer is:
blackthorn
'stick' is the definition.
(walking stick made from a blackthorn stem)
'british sailors possessing deficiency still' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in BBC).
'sailors' becomes 'RN' (abbreviation for Royal Navy).
'possessing' is an insertion indicator.
'deficiency' becomes 'lack' (synonyms).
'still' becomes 'tho' (though).
'b'+'rn'='brn'
'lack'+'tho'='lacktho'
'brn' enclosing 'lacktho' is 'BLACKTHORN'.
'getting' acts as a link.
(Other definitions for blackthorn that I've seen before include "Tree bearing sloes" , "Sloe bush" , "Sloe-bearing shrub" , "Tree producing sloes" , "A prickly thing" .)