It extended W holder (4)
I believe the answer is:
rack
'holder' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for rack that I've seen before include "Rib section of lamb" , "giving rise to anxiety" , "Storage frame; draw off (wine)" , "Support" , "Driving mist" .)