Tendon is put back in original condition (5)
I believe the answer is:
sinew
'tendon' is the definition.
(synonyms)
'is put back in original condition' is the wordplay.
'put back' shows that the letters should be reversed in order.
'in original condition' becomes 'new' (I can't explain this - if you can you should believe this answer much more).
'is' in reverse letter order is 'si'.
'si'+'new'='SINEW'
Can you help me to learn more?
(Other definitions for sinew that I've seen before include "Cord of tissue connecting muscle to bone" , "fibre" , "Force" , "As synonym for 'strength'" , "Muscular strength" .)