Ignoble foundation (4)
I believe the answer is:
base
This clue is a double definition.
'ignoble' is the first definition.
(similar in meaning)
'foundation' is the second definition.
(synonyms)
(Other definitions for base that I've seen before include "Ignoble - HQ" , "Not worth much" , "Ignoble; bottom" , "standard" , "floor" .)