Flash opening of trade fair by European displaying suitable expression (3,5)
I believe the answer is:
mot juste
'suitable expression' is the definition.
'mot juste' can be an answer for 'expression' (mot juste is a kind of expression). I am not certain of the 'suitable' bit.
'flash opening of trade fair by european' is the wordplay.
'flash opening of trade' becomes 'mot' (I can't justify this - if you can you should believe this answer much more).
'fair' becomes 'just' (synonyms).
'by' says to put letters next to each other.
'european' becomes 'e' (abbreviation e.g. EU).
'mot'+'just'+'e'='MOT JUSTE'
'displaying' is the link.
Can you help me to learn more?
(Other definitions for mot juste that I've seen before include "Highly appropriate expression" , "Exactly appropriate word" .)