Link; take part in (4)
I believe the answer is:
join
This clue is a double definition.
'link' is the first definition.
(join is a kind of link)
'take part in' is the second definition.
(thesaurus)
(Other definitions for join that I've seen before include "Associate, combine" , "ally" , "make ends meet" , "Become a member" , "Link, connect" .)