Fasten or connect (6)
I believe the answer is:
attach
This clue is a double definition.
'fasten' is the first definition.
(I know that fasten has the is a more specific form of the action attach)
'connect' is the second definition.
(I know that connect has the is a more specific form of the action enter)
(Other definitions for attach that I've seen before include "Add on to, couple" , "Join to, perhaps with staple" , "Unite?" , "Add to, connect" , "Append, affix" .)