As a companion (5)
I believe the answer is:
along
'as a companion' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for along that I've seen before include "From one end to the other" , "By the side of" , "Beside - as groups often sing!" , "Moving in a constant direction on (something)" , "(Going) in company (with others)" .)