Suit, one seen in part of West London (6)
I believe the answer is:
action
'suit' is the definition.
(synonyms)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for action that I've seen before include "Film director's cry?" , "Jarndyce and Jarndyce, say" , "instruction from director" , "Operation; engagement" , "Thing done; armed conflict" .)