CO ordered men — and one cox — on board (6,8)
I believe the answer is:
carbon monoxide
'co' is the definition.
(I've seen this before)
'ordered men and one cox on board' is the wordplay.
'ordered' indicates anagramming the letters.
'and' says to put letters next to each other.
'one' becomes 'i' (Roman numeral).
'men'+'i'+'cox'+'on'+'board'='menicoxonboard'
'menicoxonboard' with letters rearranged gives 'CARBON MONOXIDE'.
(Other definitions for carbon monoxide that I've seen before include "CO" , "Toxic gas" , "inspired to kill" , "POISON" .)