Definition of "busto"

The Entrance to the Royal Apartment is through a Vestibule, supported by Pillars, with some antick Bustoes in the Niches […]

1719, Elias Ashmole, The Antiquities of Berkshire

The Busto's he fix'd on were the Caracalla and the Cicero in the Gallery which I recommended as one of the best heads in the Gallery.

1753, Joshua Reynolds, edited by John Ingamells and John Edgcumbe, The Letters of Sir Joshua Reynolds, Yale, published 2000, page 13