Extremely rare binder for log (6)
I believe the answer is:
record
'for log' is the definition.
(I've seen this before)
'extremely rare binder' is the wordplay.
'extremely' suggests removing the centre (only the extremes of the word are used).
'binder' becomes 'cord' (I can't justify this - if you can you should believe this answer much more).
'rare' with its centre removed is 're'.
're'+'cord'='RECORD'
Can you help me to learn more?
(Other definitions for record that I've seen before include "Log - so far unsurpassed" , "Note - disc" , "It provides evidence" , "Best known performance in sport" , "Written account (none better!)" .)