Support the unusual seer (7)
I believe the answer is:
prophet
'seer' is the definition.
(thesaurus)
'support the unusual' is the wordplay.
'support' becomes 'prop' (prop is a kind of support).
'unusual' indicates anagramming the letters.
'the' is an anagram of 'het'.
'prop'+'het'='PROPHET'
(Other definitions for prophet that I've seen before include "Prognosticator" , "Predictor of the future" , "Say, Cassandra" , "Visionary" , "Augur" .)