Main alternative to paper clip? (6)
I believe the answer is:
staple
This clue is a double definition.
'main' is the first definition.
(I've seen this before)
'alternative to paper clip?' is the second definition.
(staples and paper clips both secure paper)
(Other definitions for staple that I've seen before include "Fundamental" , "key" , "Clip" , "Main - way to fasten paper" , "Fastening wire" .)