Passing pointer on European trail (10)
I believe the answer is:
evanescent
'passing' is the definition.
(I've seen this before)
'pointer on european trail' is the wordplay.
'pointer' becomes 'vane' (a weathervane points).
'on' says to put letters next to each other.
'european' becomes 'e' (abbreviation e.g. EU).
'trail' becomes 'scent' (an animal's trail is its scent).
'vane' after 'e' is 'evane'.
'evane'+'scent'='EVANESCENT'
(Other definitions for evanescent that I've seen before include "Fleeting" , "Passing" , "slipping away" , "Transient" , "evaporating slowly" .)