Without foundation (8)
I believe the answer is:
baseless
'without foundation' is the definition.
('foundation' can be 'base' (synonyms) so maybe 'without foundation' can be ''baseless')
This is all the clue.
(Other definitions for baseless that I've seen before include "Without foundation, as rumours may be" , "Wrong, as a matter of fact" , "Without foundation or substance" , "Idle" , "Without foundation, unsupported" .)