Artist takes jetty to be a weapon (6)
I believe the answer is:
rapier
'a weapon' is the definition.
(rapier is a kind of weapon)
'artist takes jetty' is the wordplay.
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'takes' is a charade indicator (letters next to each other).
'jetty' becomes 'pier' (I've seen this before).
'ra'+'pier'='RAPIER'
'to be' is the link.
(Other definitions for rapier that I've seen before include "Narrow sword with two-edged blade" , "Sword for thrusting" , "Thin sharp sword" , "Long slender sword" , "Fine-bladed sword" .)