All of the tarot cards are associated with the four ancient elements — earth, air, fire, or water.
The Fool is associated with the element of air. Normally, that association stems from complicated astrological and kabbalistic formulations.
I just learned, though, that the Fool’s association with air could be based in ordinary language, too. The American Heritage Dictionary describes the connection:
The pejorative nature of the term fool is strengthened by a knowledge of its etymology. Its source, the Latin word follis, meant “a bag or sack, a large inflated ball, a pair of bellows.” Users of the word in Late Latin, however, saw a resemblance between the bellows or the inflated ball and a person who was what we would call “a windbag” or “an airhead.” The word, which passed into English by way of French, is first recorded in English in a work written around the beginning of the 13th century with the sense “a foolish, stupid, or ignorant person.”
Source: The American Heritage® Dictionary of the English Language, Fourth Edition. Copyright © 2000 by Houghton Mifflin Company. Published by the Houghton Mifflin Company. All rights reserved.