Complete stop as outsiders leave — speech unfinished (5)
I believe the answer is:
total
'complete' is the definition.
(synonyms)
'stop as outsiders leave speech unfinished' is the wordplay.
'as outsiders leave' says to take the centre (the letters on the outside leave).
'speech' becomes 'talk' (talk is a kind of speech).
'unfinished' means to remove the last letter.
The centre of 'stop' is 'to'.
'talk' with its final letter taken away is 'tal'.
'to'+'tal'='TOTAL'
(Other definitions for total that I've seen before include "gross" , "Unqualified" , "Complete sum" , "The whole, sum" , "Comprehensive" .)