unsubstantial
Concise Oxford English Dictionary © 2008 Oxford University Press:
unsubstantial/ʌnsəbˈstanʃ(ə)l/
▶adjective having little or no solidity, reality, or factual basis.
– derivatives
unsubstantiality noun,
unsubstantially adverb.
unsubstantiality noun,
unsubstantially adverb.
'unsubstantial' also found in these Oxford entries:

