Opening track track track (5)
I believe the answer is:
trail
'track' is the definition.
(I know that trail is a type of track)
'opening track track' is the wordplay.
'opening' suggests taking the first letters.
'track' becomes 'rail' (synonyms).
The first letter of 'track' is 't'.
't'+'rail'='TRAIL'
(Other definitions for trail that I've seen before include "Follow - track" , "Rural footpath" , "Beaten path; track" , "Scent or track followed in hunting" , "Dog - track" .)