A foundation is corrupt (5)

I believe the answer is:

abase

'is corrupt' is the definition.
(thesaurus)

'a foundation' is the wordplay.
'foundation' becomes 'base' (synonyms).
'a'+'base'='ABASE'

(Other definitions for abase that I've seen before include "put to shame" , "Lower" , "what 11 [REPRIMANDS] are meant to do" , "Degrade (oneself)" , "Humiliate" .)

I've seen this clue in The Mirror.

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