[rock.er] n (1760) 1 a: either of two curving pieces of wood or metal on which an object (as a cradle) rocks b: any of various objects (as a rocking chair or an infant's toy having a seat placed between side pieces) that rock on rockers c: any of various objects in the form of a rocker or with parts resembling a rocker (as a skate with a curved blade) d (1): any of the curved stripes at the lower part of a chevron worn by a noncommissioned officer above the rank of sergeant (2): the curved stripe at the upper part of a chevron worn by a chief petty officer
2: any of various devices that work with a rocking motion
3: a rock performer, song, or enthusiast -- off one's rocker : in a state of extreme confusion or insanity "went off her rocker, and had to be put away --Mervyn Wall"