Pay, mind, for piece of extra information? (8)
I believe the answer is:
footnote
'piece of extra information?' is the definition.
(a footnote adds extra information)
'pay mind' is the wordplay.
'pay' becomes 'foot' (as in footing the bill).
'mind' becomes 'note' (mind can mean to note or be aware of something).
'foot'+'note'='FOOTNOTE'
'for' acts as a link.
(Other definitions for footnote that I've seen before include "Too often (anag.)" , "It's not very important" , "Comment at bottom of page" , "Text at page end" , "Explanation at bottom of page" .)