Support the bad seer (7)
I believe the answer is:
prophet
'seer' is the definition.
(I know that prophet is a type of diviner)
'support the bad' is the wordplay.
'support' becomes 'prop' (prop up can mean to support).
'bad' is an anagram indicator.
'the' is an anagram of 'het'.
'prop'+'het'='PROPHET'
(Other definitions for prophet that I've seen before include "One speaks by divine inspiration" , "One who foretells the future as in the Bible" , "Divine spokesman or forecaster" , "Biblical seer" , "Foreteller" .)