One providing thrust in either direction (5)
I believe the answer is:
rotor
'direction' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'one providing thrust in either' is the wordplay.
'one providing thrust in' becomes 'rot' (I can't explain this - if you can you should give a lot more credence to this answer).
'either' becomes 'or' (I've seen this in another clue).
'rot'+'or'='ROTOR'
Can you help me to learn more?
(Other definitions for rotor that I've seen before include "Distributor arm" , "Revolving part of turbine" , "Machine part that turns around" , "Revolving component" , "Palindromic revolving part of machine" .)