Blue net for example one used to catch nothing (9)
I believe the answer is:
woebegone
'blue' is the definition.
(thesaurus)
'net for example one used to catch nothing' is the wordplay.
'net' becomes 'web' (synonyms).
'for example' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'used to catch' is an insertion indicator (inserted letters are caught inside).
'nothing' becomes 'O' (O resembles 0).
'web'+'eg'+'one'='webegone'
'webegone' enclosing 'o' is 'WOEBEGONE'.
(Other definitions for woebegone that I've seen before include "dismal look" , "Looking sad" , "Sad, miserable" , "Miserable-looking" , "forlorn state" .)