Land with one on board (5)
I believe the answer is:
pilot
'land' is the definition.
Both the definition and answer are adjectives. Perhaps there's an association between them I don't understand?
'one on board' is the wordplay.
I cannot really understand how this works, but
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
The remaining letters 'plot' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
'with' is the link.
(Other definitions for pilot that I've seen before include "Plane flier" , "trial episode" , "Plane flyer" , "Steer (a ship or plane)" , "Plane driver" .)