Notice second empty pasty (3)
I believe the answer is:
spy
'notice' is the definition.
(thesaurus)
'second empty pasty' is the wordplay.
'second' becomes 's' (common abbreviation).
'empty' says to hollow out the word (remove centre letters).
'pasty' with its centre taken out is 'py'.
's'+'py'='SPY'
(Other definitions for spy that I've seen before include "Watch covertly like secret agent" , "Discover" , "Catch sight of" , "Person who secretly collects information as for government" , "Undercover agent" .)