At printer's, measures editor's initial written submission (3)
I believe the answer is:
ems
'at printer's measures editor's initial written submission' is the definition.
I can't judge whether this definition defines the answer.
'at printer's measures editor's initial' is the wordplay.
'at' means one lot of letters go next to another.
'printer's measures' becomes 'ms' (I can't explain this - if you can you should believe this answer much more).
'initial' suggests taking the first letters.
The first letter of 'editors' is 'e'.
'ms' after 'e' is 'EMS'.
Can you help me to learn more?
(Other definitions for ems that I've seen before include "German spa; print measures" , "German river" , "German city" , "Printers' measures" , "Measurement units in printing" .)