Resin you once put back to inhibit disease (5)
I believe the answer is:
epoxy
'resin' is the definition.
(epoxy is a kind of resin)
'you once put back to inhibit disease' is the wordplay.
'you once' becomes 'ye' (historical version of 'you').
'put back' shows that the letters should be reversed in order.
'to inhibit' indicates putting letters inside.
'disease' becomes 'pox' (pox is a kind of disease).
'ye' backwards is 'ey'.
'ey' going around 'pox' is 'EPOXY'.
(Other definitions for epoxy that I've seen before include "Type of resin" , "Synthetic adhesive, paint etc." , "Synthetic resin used as glue" , "Type of adhesive/paint" , "Adhesive; plastic" .)