Quartet heard and observed as anticipated (8)
I believe the answer is:
foreseen
'anticipated' is the definition.
(thesaurus)
'quartet heard and observed' is the wordplay.
'quartet' becomes 'four' ('four' can be a synonym of 'quartet').
'heard' shows a homophone (sound like).
'and' says to put letters next to each other.
'observed' becomes 'seen' ('seen' can be a synonym of 'observed'**).
'four' sounds like 'fore'.
'fore'+'seen'='FORESEEN'
'as' acts as a link.
(Other definitions for foreseen that I've seen before include "Envisaged" , "Expected" , "Predicted" , "Anticipated" , "No surprise" .)