Baluster

A baluster— also called spindle or stair stick—is a moulded shaft, square or of lathe-turned form, a form cut from a rectangular or square plank, one of various forms of spindle in woodwork, made of stone or wood and sometimes of metal, standing on a unifying footing, and supporting the coping of a parapet or the handrail of a staircase.

Multiplied in this way, they form a balustrade. Individually, a baluster shaft may describe the turned form taken by a brass or silver candlestick, an upright furniture support, or the stem of a brass chandelier, etc.

According to OED, "baluster" is derived through the French: balustre, from Italian: balaustro, from balaustra, "pomegranate flower" [from a resemblance to the swelling form of the half-open flower (illustration, below left)], from Latin balaustium, from Greek balaustion-βαλαύστιον.

The earliest examples are those shown in the bas-reliefs representing the Assyrian palaces, where they were employed as window balustrades and apparently had Ionic capitals. As an architectural element the balustrade did not seem to have been known to either the Greeks or the Romans, but baluster forms are familiar in the legs of chairs and tables represented in Roman bas-reliefs, where the original legs or the models for cast bronze ones were shaped on the lathe, or in Antique marble candelabra, formed as a series of stacked bulbous and disc-shaped elements, both kinds of sources familiar to Quattrocento designers.

The application to architecture was a feature of the early Renaissance: late fifteenth-century examples are found in the balconies of palaces at Venice and Verona. These quattrocento balustrades are likely to be following yet-unidentified Gothic precedents. They form balustrades of colonnettes as an alternative to miniature arcading.

...
Wikipedia