Hundreds of quantities of paper, one imagines (6)
I believe the answer is:
dreams
'one imagines' is the definition.
(I've seen this in another clue)
'hundreds of quantities of paper' is the wordplay.
I cannot really see how this works, but
'hundreds' could be 'd' (I've seen this in other clues) and 'd' is found within the answer.
'quantities' could be 'reams' (ream is a kind of quantity) and 'reams' is present in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for dreams that I've seen before include "Reveries or cherished aspirations" , "Thoughts and visions during sleep" , "Imaginings" , "Fantasy ambitions" , "'''We are such stuff as ... are made on'' The Tempest (6)'" .)