Rock band opening a season (6)
I believe the answer is:
basalt
'rock' is the definition.
(basalt is a kind of rock)
'band opening a season' is the wordplay.
'opening' says to take the initial letters.
'season' becomes 'salt' (salting is a kind of seasoning**).
The first letter of 'band' is 'b'.
'b'+'a'+'salt'='BASALT'
(Other definitions for basalt that I've seen before include "Common volcanic rock" , "Dark rock of volcanic origin" , "Commonest type of solidified lava; dense, dark grey and fine-grained" , "rock from 2 [VOLCANO]" , "Rock containing olivine" .)