Signify agreement to interrupt live number (7)
I believe the answer is:
betoken
'signify' is the definition.
(I've seen this before)
'agreement to interrupt live number' is the wordplay.
'agreement' becomes 'ok' (I've seen this in other clues).
'to interrupt' means one lot of letters goes inside another.
'live' becomes 'be' (synonyms).
'number' becomes 'ten' (ten is a kind of whole number).
'be'+'ten'='beten'
'ok' put inside 'beten' is 'BETOKEN'.
(Other definitions for betoken that I've seen before include "Signify" , "Be a sign of (poet,)" , "Be a warning sign of (an event)" , "Show by a sign, indicate" , "Be a sign of (something)" .)