Tentative approach (8)
I believe the answer is:
overture
'tentative approach' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for overture that I've seen before include "Introductory piece" , "Pre-curtain-up piece" , "Orchestral opener" , "Approach - musical introduction" , "Musical prelude to opera or ballet" .)