Imaginary, illusory, intangible; not real.

Not existing in substance or reality; not real; imaginary, illusive; non-substantial.

Of the nature of a chimera; vainly or fantastically conceived, imaginary, fanciful, visionary.

= chimerical, adj.; imaginary, fanciful.

= chimeric, adj.

Negative; involving or characterized by negation.

(un-, prefix1 affix 1.)