In connection, link one top-class relative (7)
I believe the answer is:
liaison
'in connection' is the definition.
'liaison' can be an answer for 'connection' (I've seen this in another clue). I am not sure about the 'in' bit.
'link one top-class relative' is the wordplay.
'link' becomes 'l' (this could be a standard abbreviation I've not previously seen).
'one' becomes 'i' (Roman numeral).
'top-class' becomes 'ai' (resembles Al, informal term for top quality).
'relative' becomes 'son' (son is a type of relative').
'l'+'i'+'ai'+'son'='LIAISON'
Can you help me to learn more?
(Other definitions for liaison that I've seen before include "Sort of officer" , "A contact or affair" , "Association" , "Connection - relationship" , "Contact between groups" .)