eccentric

An eccentric is a person or thing that deviates from what is ordinary or expected. As an adjective, eccentric describes behavior, style, or appearance that is unconventional or unusual. The term can be neutral or mildly positive, but it can also imply quirkiness or unconventionality.

Etymology: The word derives from the Greek ekkentros, meaning out of center, from ek- 'out' + kentron 'center.'

In geometry, eccentricity measures how much a conic section deviates from a circle. For circles, e equals 0; 0 < e < 1 describes an ellipse; e = 1 describes a parabola; e > 1 describes a hyperbola. In astronomy and orbital mechanics, orbital eccentricity similarly describes the shape of a body's path around another body: e near 0 is nearly circular; higher e indicates a more elongated orbit; e ≥ 1 corresponds to parabolic or hyperbolic trajectories.

In engineering and mechanics, an eccentric is a shaft-mounted offset used to convert rotary motion to linear motion, such as an eccentric pin or an eccentric cam. It is a standard component in pumps, engines, and other machines.

In physiology, an eccentric contraction refers to a muscle lengthening under tension, such as controlling the descent of a weight.

In everyday language, describing someone as eccentric suggests unusual or distinctive behavior that is not typically harmful and may be seen as creative or idiosyncratic.