1620s, "place of combat," from Latin harena "place of combat, enclosed space in the middle of Roman amphitheaters," originally "sand, sandy place" (source also of Spanish arena, Italian rena, French arène "sand"), a word of uncertain origin, perhaps from Etruscan. The central stages of Roman amphitheaters were strewn with sand to soak up the blood. Figuratively, "scene of contest of any kind" by 1814.
1640s, "sandy," from Latin arenaceus, harenaceus, from harena "sand, sandy place" (see arena). The figurative sense of "dry" is attested from 1870.
occasional plural suffix of words ending in -a (see a- (1)), most of which, in English, are from Latin nominative fem. singular nouns (or Greek ones brought up through Latin), which in Latin form their plurals in -ae. But plurals in native -s were established early in English for many of them (such as idea, arena) and many have crossed over since. Purity now would only breed monsters.
1743, in architecture, "raised platform around an ancient arena" (upon which sat persons of distinction), also "projecting base of a pedestal," from Latin podium "raised platform," from Greek podion "foot of a vase," diminutive of pous (genitive podos) "foot," from PIE root *ped- "foot." Meaning "raised platform at the front of a hall or stage" is by 1947.
The Greek word was applied by the stoics to the controlling of the appetites and passions as the path to virtue and was picked up from them by the early Christians. Figurative sense of "unduly strict or austere" also is from 1640s. Related: Ascetical (1610s).
to win something hands down (1855) is from horse racing, from a jockey's gesture of letting the reins go loose in an easy victory.
The Two Thousand Guinea Stakes was not the best contested one that it has been our fortune to assist at. ... [T]hey were won by Meteor, with Scott for his rider; who went by the post with his hands down, the easiest of all easy half-lengths. Wiseacre certainly did the best in his power to spoil his position, and Misdeal was at one time a little vexatious. [The Sportsman, report from April 26, 1840]
Ancient Greek had akoniti "without a struggle, easily," from akonitos (adj.), literally "without dust," specifically "without the dust of the arena."