Emily Dickinson Lexicon

PHAN'TASM, n. [Gr. φαντασμα, from φανταζω, to show, from the root of φαινω, to shine; φαινομαι, to appear.]

That which appears to the mind; the image of an external object; hence, an idea or notion. It usually denotes a vain or airy appearance; something imagined. All the interim is / Like a phantasm or a hideous dream. – Shak.