Top of the bill, yours truly (4)
I believe the answer is:
acme
'top' is the definition.
(synonyms)
'bill yours truly' is the wordplay.
'bill' becomes 'ac' (short for account).
'yours truly' becomes 'me' (the person who set this crossword).
'ac'+'me'='ACME'
'of the' is the link.
(Other definitions for acme that I've seen before include "Highest point of excellence or achievement" , "Summit of achievement" , "Highest level or degree attainable" , "Culminating point" , "Peak of perfection" .)