Interconnected group (7)
'interconnected group' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for network that I've seen before include "(Eg, railway) system" , "broadcasting group" , "Consonant like f, th" , "Organisation" , "Group of transport routes" .)
(Other definitions for nexus that I've seen before include "Unsex (anag.); a bond" , "Connecting bond" , "Connecting band" , "Bond, connected group" , "line" .)