The term 'wingnut' is a transparent compound formed within Modern English from two native Germanic elements. The first element, 'wing', draws on the familiar shape of a bird's wing to metaphorically describe the two flat, projecting tabs on the fastener, which allow it to be turned by hand. The second element, 'nut', specifies its functional category as a threaded fastener. The slang meaning, originating in late 20th-century American English, is a metaphorical extension, likening a person with rigid, extreme views to a fixed mechanical part that is difficult to turn or change.

Structure: wing (projection) + nut (fastener) - wing: From Old English wenge (wing of a bird), of Germanic origin. In this compound, it functions metaphorically to denote a projecting, wing-like part. - nut: From Old English hnutu, of Germanic origin. It functions as the core element, specifying the object is a type of fastener.