Definify.com

Webster 1913 Edition

Adj.

Lacking in matter or substance; visionary; chimerical.

, a.

Not substantial; not solid.

Not real; not having substance.

unsubstantial ‎(comparative more unsubstantial, superlative most unsubstantial)

(archaic) Alternative form of insubstantial
- 1859, Charles Dickens, A Tale of Two Cities
  They shook hands upon it, and Sydney turned away. Within a minute afterward he was, to all outward appearance, as unsubstantial as ever.