plano-

word-forming element meaning "level, flat, plane," from Latin plani-, from planus "flat, level" (from PIE root *pele- (2) "flat; to spread").

late Old English planete, in old astronomy, "star other than a fixed star; star revolving in an orbit," from Old French planete (Modern French planète) and directly from Late Latin planeta, from Greek planētēs, from (asteres) planētai "wandering (stars)," from planasthai "to wander," a word of uncertain etymology.

Perhaps it is from a nasalized form of PIE root *pele- (2) "flat; to spread," on the notion of "spread out," "but the semantics are highly problematic," according to Beekes, who notes the similarity of meaning to Greek plazein "to make devious, repel, dissuade from the right path, bewilder," but adds, "it is hard to think of a formal connection."

So called because they have apparent motion, unlike the "fixed" stars. Originally including also the moon and sun but not the Earth; modern scientific sense of "world that orbits a star" is from 1630s in English. The Greek word is an enlarged form of planes, planetos "who wanders around, wanderer," also "wandering star, planet," in medicine "unstable temperature."

*pelə-, Proto-Indo-European root meaning "flat; to spread."

It forms all or part of: airplane; dysplasia; ectoplasm; effleurage; esplanade; explain; explanation; feldspar; field; flaneur; floor; llano; palm (n.1) "flat of the hand;" palm (n.2) "tropical tree;" palmy; piano; pianoforte; plain; plan; planar; Planaria; plane (n.1) "flat surface;" plane (n.3) "tool for smoothing surfaces;" plane (v.2) "soar, glide on motionless wings;" planet; plani-; planisphere; plano-; -plasia; plasma; plasmid; plasm; -plasm; -plast; plaster; plastic; plastid; -plasty; Polack; Poland; Pole; polka; protoplasm; veldt.

It is the hypothetical source of/evidence for its existence is provided by: Greek plassein "to mold," plasma "something molded or created;" Latin planus "flat, level, even, plain, clear;" Lithuanian plonas "thin;" Celtic *lanon "plain;" Old Church Slavonic polje "flat land, field," Russian polyi "open;" Old English feld, Middle Dutch veld "field."