Rex turned up nose at leader in Evening Echo (8)
I believe the answer is:
resonate
'echo' is the definition.
(I've seen this before)
'rex turned up nose at leader in evening' is the wordplay.
'rex' becomes 'r' (common abbreviation e.g. GR=George Rex, King Georg).
'turned up' says the letters should be written backwards.
'leader in' suggests taking the first letters.
The first letter of 'evening' is 'e'.
'nose' written backwards gives 'eson'.
'r'+'eson'+'at'+'e'='RESONATE'
(Other definitions for resonate that I've seen before include "Produce a reverberating sound" , "Echo" , "Resound" , "Sound deeply and clearly" , "Ring; meet with agreement" .)