"lying in or otherwise related to a plane, flat," 1850, from Latin planaris "level, flat," from planum "plane" (from PIE root *pele- (2) "flat; to spread"). An earlier word in the same sense was planary (1660s).
Entries linking to planar
*pele- 2
*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."
biplanar adj.
"lying or situated in two planes," 1849; see bi- "two" + planar.
coplanar adj.
also co-planar, "situated or operating in the same plane," 1849, from co- + planar.