'Space cadet' definitions:

Definition of 'space cadet'

From: WordNet
noun
Someone who seems unable to respond appropriately to reality (as if under the influence of some narcotic drug)

Definition of 'Space cadet'

From: GCIDE
  • Space cadet \Space cadet\, n. a person who appears disconnected from reality, or living in his own world; -- sometimes used of people who are under the influence of mind-altering drugs. [derogatory] [PJC]