1 a: a sudden and odd or seemingly pointless idea or turn of the mind b: a seemingly capricious action or event 2archaic: a whimsical quality or disposition 3: one that is markedly unusual or abnormal: as a: a person or animal having a physical oddity and appearing in a circus sideshow bslang(1): a sexual deviate (2): a person who uses an illicit drug c:hippied: an atypical postage stamp usually caused by a unique defect in paper (as a crease) or a unique event in the manufacturing process (as a speck of dirt on the plate) that does not produce a constant or systematic effect 4 a: an ardent enthusiast <film freaks>b: a person who is obsessed with something <a control freak>