Main way to fix printed sheets together (6)
I believe the answer is:
staple
'main' is the definition.
(I've seen this before)
'way to fix printed sheets together' is the wordplay.
I cannot quite understand how this works, but
'way' could be 'st' (abbreviation for street) and 'st' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for staple that I've seen before include "Principle - metal fastener" , "key" , "The food one normally eats" , "Fasten with short U-shaped bits of wire" , "Basic element" .)