convex

Etymology

Borrowed from Middle French convexe, from Latin convexus (“arched”).

adj

1. Curved or bowed outward like the outside of a bowl, circle, or sphere.
2. (functional analysis, not comparable, of a real-valued function on the reals) having an epigraph that is a convex set.
3. (geometry, not comparable, of a polygon) having no internal angles greater than 180 degrees.
4. (mathematics, not comparable, of a set in Euclidean space) arranged such that for any two points in the set, a straight line between the two points is contained within the set.

noun

1. Any convex body or surface.
   Half heaven's convex glitters with the flame. 1714, Royal Progress, Thomas Tickell
2. (gambling) A playing card made convex for use in cheating.
   Coordinate term: concave
3. (gambling) A small convex mirror used to cheat by observing other players' cards.
   Of all the devices for defrauding at poker, the “shiner,” or “convex” […] Modern convexes are also considerably larger than those of former days. 2019, John Philip Quinn, Fools of Fortune; or, Gambling and Gamblers