space cadet

Etymology
From the title of the 1948 juvenile science fiction novel Space Cadet, by Robert Heinlein.

Noun

 * 1)  A person in training to be a (generally military) astronaut, especially in science fiction.
 * 2)  One who deals with reality in a way consistent with being under the influence of (or "spaced out on") drugs.
 * 3)  One who forgets, daydreams, or otherwise is distracted from reality more often than most.
 * 1)  One who forgets, daydreams, or otherwise is distracted from reality more often than most.