noun

• The act of wandering; deviation from truth, moral rectitude; abnormal; divergence from the straight, correct, proper, normal, or from the natural state.
• (optics) The convergence to different foci, by a lens or mirror, of rays of light emanating from one and the same point, or the deviation of such rays from a single focus; a defect in a focusing mechanism that prevents the intended focal point.
• (astronomy) A small periodical change of the apparent positions of the stars and other heavenly bodies, due to the combined effect of the motion of light and the motion of the observer.
• (astronomy, by extension) The tendency of light rays to preferentially strike the leading face of a moving object (the effect underlying the above phenomenon).
• A partial alienation of reason.
• (fantasy, roleplaying games) Any creature with supernatural powers not found in the organized classes of beings in a given setting.
• A mental disorder, especially one of a minor or temporary character.
• (zoology, botany) Atypical development or structure; deviation from the normal type; an aberrant organ.
• (medicine) A deviation of a tissue, organ or mental functions from what is considered to be within the normal range.
• (electronics) A defect in an image produced by an optical or electrostatic lens system.