Boot out old Brazilian captain unable to finish (5)
I believe the answer is:
expel
'boot out' is the definition.
(synonyms)
'old brazilian captain unable to finish' is the wordplay.
I cannot quite see how this works, but
'old' could be 'ex' (prefix meaning former or onetime) and 'ex' is found within the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for expel that I've seen before include "Possibly remove from club" , "Drive out with force" , "Force to leave" , "Eject (from school)" , "Get rid" .)