An explorer could back a roué (5)
I believe the answer is:
drake
'an explorer' is the definition.
(I know that Drake is a navigator)
'could back a roue' is the wordplay.
'back' indicates one should take the final letters.
'a roue' becomes 'rake' ('rake' can be a synonym of 'roue').
The final letter of 'could' is 'd'.
'd'+'rake'='DRAKE'
(Other definitions for drake that I've seen before include "Aquatic bird" , "Male bird" , "adventurer from Devon" , "world traveller" , "Male water-bird" .)