Discussion expected to secure one a diary (8)
I believe the answer is:
dialogue
'discussion' is the definition.
(I've seen this before)
'expected to secure one a diary' is the wordplay.
'expected' becomes 'due' (I've seen this before).
'to secure' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'diary' becomes 'log' (I've seen this before).
'i'+'a'+'log'='ialog'
'due' enclosing 'ialog' is 'DIALOGUE'.
(Other definitions for dialogue that I've seen before include "Discussion" , "Two-way conversation" , "part of play one can't perform" , "Talks" , "The words spoken by characters in a play" .)