A doubter caught out being sterile (7)
I believe the answer is:
aseptic
'sterile' is the definition.
(I know that sterile can be written as aseptic)
'a doubter caught out' is the wordplay.
'doubter' becomes 'sceptic' (synonyms).
'caught' becomes 'c' (cricket abbreviation).
'out' is a deletion indicator.
'sceptic' with 'c' taken away is 'septic'.
'a'+'septic'='ASEPTIC'
'being' acts as a link.
(Other definitions for aseptic that I've seen before include "Free from harmful bacteria" , "ideal conditions for hospital?" , "Paciest (anag.)" , "Sterile" , "Free from bacteria, surgically clean" .)