Link, connection (5)
I believe this clue is a double definition.
'link' is the first definition.
(I know that link can be written as nexus)
'connection' is the second definition.
(I know that nexus is a type of linkage)
(Other definitions for nexus that I've seen before include "Connected series; central point" , "Link, connection" , "Connecting band" , "Bond; linked group" , "Focal point; link" .)
I believe this is a double definition.
'link' is the first definition.
(I know that tie up is a kind of attach)
'connection' is the second definition.
(I've seen this before)
(Other definitions for tie-up that I've seen before include "Link, connection" , "Association" , "Tether" , "Link (between companies)" , "Secure with ropes" .)