Ointment not to waste left hidden (5)
I believe the answer is:
salve
'ointment' is the definition.
(synonyms)
'not to waste left hidden' is the wordplay.
'not to waste' becomes 'save' (to save something is to stop it going to waste).
'left' becomes 'L' (common abbreviation).
'hidden' indicates putting letters inside.
'save' placed around 'l' is 'SALVE'.
(Other definitions for salve that I've seen before include "Soothing ointment - may also be applied to feelings" , "Healing ointment" , "healer" , "Balm - ointment" , "comfort" .)