an artificial cloud created by an aircraft; caused either by condensation due to the reduction in air pressure above the wing surface or by water vapo more..an artificial cloud created by an aircraft; caused either by condensation due to the reduction in air pressure above the wing surface or by water vapor in the engine exhaust(noun.object)
(astronomy) the luminous cloud of particles surrounding the frozen nucleus of a comet; forms as the comet approaches the sun and is warmed (noun.object)