Join fleet on bearing to the north (6)
I believe the answer is:
fasten
'join' is the definition.
(thesaurus)
'fleet on bearing to the north' is the wordplay.
'fleet' becomes 'fast' ('fast' can be similar in meaning to 'fleet').
'on' is a charade indicator (letters next to each other).
'bearing' becomes 'ne' (**).
'to the north' says the letters should be written in reverse.
'ne' in reverse letter order is 'en'.
'fast'+'en'='FASTEN'
(Other definitions for fasten that I've seen before include "Close, make secure" , "Attach" , "Tie or join together, fix firmly" , "Nail" , "Tie, secure" .)