Schedule a meeting ultimately to terminate head of accounts (6)
I believe the answer is:
agenda
'schedule' is the definition.
(synonyms)
'a meeting ultimately to terminate head of accounts' is the wordplay.
'ultimately' indicates one should take the final letters.
'to terminate' becomes 'end' ('end' can be a synonym of 'terminate').
'head of' says to take the initial letters.
The final letter of 'meeting' is 'g'.
The initial letter of 'accounts' is 'a'.
'a'+'g'+'end'+'a'='AGENDA'
(Other definitions for agenda that I've seen before include "Scheme" , "Table of business" , "Something perhaps hidden" , "Schedule, order of business" , "things to discuss" .)