They join the course (5)
I believe the answer is:
links
'they' is the definition.
Both the definition and answer are plural nouns.
Perhaps they are linked in a way I don't understand?
'join the course' is the wordplay.
'join' becomes 'link' (synonyms).
'the course' becomes 's'.
'link'+'s'='LINKS'
Can you help me to learn more?
(Other definitions for links that I've seen before include "Where golfers play" , "Seaside golf course - parts of a chain" , "chains" , "Connects, ties in" , "course for sportspeople" .)