Number of sheets — about a thousand? (4)
I believe the answer is:
ream
'number of sheets' is the definition.
'ream' can be an answer for 'sheets' (I've seen this before). I am not sure about the 'number of' bit.
'aeur about a thousand?' is the wordplay.
I cannot quite see how this works, but
'about' could be 'rea' (I've seen this in other clues) and 'rea' is present in the answer.
'thousand?' could be 'm' (Roman numeral for a thousand) and 'm' is found in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ream that I've seen before include "Widen (hole) with borer; twenty quires" , "20 quires of paper" , "Widen (hole); quantity of paper" , "500 sheets, perhaps" , "Many bits of paper" .)