Clip on or staple (6)
I believe the answer is:
attach
This clue is a double definition.
'clip on' is the first definition.
(I've seen this in another clue)
'staple' is the second definition.
(I've seen this in another clue)
(Other definitions for attach that I've seen before include "Append, add on to" , "Join, connect" , "Tie, bind to" , "Conjoin, affix" , "Associate" .)