Why is the ninth month called September?
1650s, from Latin pneumaticus "of the wind, belonging to the air," from Greek pneumatikos "of wind or air" (which is attested mainly as "of spirit, spiritual"), from pneuma (genitive pneumatos) "the wind," also "breath" (see pneuma). Earlier was pneumatical (c.1600).
pneumatic pneu·mat·ic (nōō-māt'ĭk, nyōō-)
Of or relating to air or other gases.
Relating to respiration.
Relating to a structure that is filled with air.