Adamant

The word adamant appears in Part three, chapter three of Gulliver's Travels a total of nine times. In this chapter Gulliver gives us a very complicated description of the mechanics of the floating island of Laputa. He describes the bottom of the island as being made of a "plate of adamant" and the loadstone that allows the island to move also contains "a very strong axle of adamant passing through its middle." The repeated use of the word adamant emphasizes the strength of the island and the king's ability to crush the citizens of Laputa. However, as Gulliver notes, the king would never exert the full strength of the island "for fear of breaking the Adamantine Bottom" which would cause their whole society to fall apart.

According to the OED adamant is derived from Old English and originally meant: "a hard, strong rock, or mineral, not otherwise identified, to which various other (often contradictory) properties were attributed; in later use chiefly a poetical or rhetorical name for: an embodiment of surpassing hardness". Today we usually use adamant to mean "refusing to be persuaded or to change one's mind". By the 17th century it was used in the scientific community as a synonym of diamond.

Using ECCO I searched for "adamant" with the limiter "publication date 1720-1730" and received 289 results. Most of them were under the subjects literature and language (179) and religion and philosophy (68). One of the books mentioned, Thoughts of a Project for Draining the Irish Channel, was written in 1722 and is described as a satire on the South-Sea Scheme. This is probably a reference to the South Sea Trading Company of Great Britain that was granted a trade monopoly in South America. I found other references to adamant in Swift's Second Collection of Miscellanies and Milton's Paradise Lost.