"triumphant, flourishing," literally "worthy of the palm" (of victory or triumph), c. 1600, from palm (n.2) in the "triumph" sense + -y (2). The meaning "full of palms" attested from 1660s.
Entries linking to palmy
palm n.2
tropical tree of the order Palmae; the date-palm, Middle English palme, from Old English palma, Old French palme, both from Latin palma "palm tree," originally "palm of the hand;" the tree so called from the shape of its leaves, like fingers of a hand (see palm (n.1)).
The word traveled early to northern Europe, where the tree does not grow, via Christianity, and took root in the local languages (such as Old Saxon palma, Old High German palma, Old Norse palmr); Palm Sunday, the Sunday before Easter, commemorating Christ's triumphal entry into Jerusalem, is Old English palm-sunnandæg. In ancient times, a leaf or frond of the palm was carried or worn as a symbol of victory or triumph, or on feast days; hence figurative use of palm for "victory, triumph" (late 14c.).
Palm Beach, Florida, named for the palm groves there, was established as a luxury resort c. 1900 by railroad magnate Henry Flagler. Palm court "large room in a hotel, etc., usually decorated with potted palms" is recorded by 1908.
-y 2
adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Originally added to nouns in Old English; used from 13c. with verbs, and by 15c. even with other adjectives (for example crispy). Adjectives such as hugy, vasty are artificial words that exist for the sake of poetical metrics.
*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."