Engineers' morning paper? (4)
I believe the answer is:
ream
'paper?' is the definition.
(I've seen this before)
'engineers' morning' is the wordplay.
'engineers'' becomes 'RE' (Royal Engineers).
'morning' becomes 'am'.
're'+'am'='REAM'
(Other definitions for ream that I've seen before include "Widen (hole); quantity of paper" , "516 sheets of paper" , "20 quires of paper" , "Twenty quires of paper" , "Lots of paper" .)