Tetrad times two (5)
I believe the answer is:
octet
'tetrad times two' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for octet that I've seen before include "Music for eight" , "Played" , "Group that plays" , "A number of musicians" , "Mendelssohn or Schubert piece" .)