Buzz following check, initially, and mate (4)
I believe the answer is:
chum
'mate' is the definition.
(thesaurus)
'buzz following check initially' is the wordplay.
'buzz' becomes 'hum' ('hum' can be a synonym of 'buzz').
'following' means one lot of letters go next to another.
'initially' indicates taking the first letters.
The first letter of 'check' is 'c'.
'hum' after 'c' is 'CHUM'.
'and' acts as a link.
(Other definitions for chum that I've seen before include "Salmon" , "Close friend (colloq.)" , "Pal, buddy" , "Pal, mate" , "Informally, a close friend" .)