Mononym

The atlas and axis have special names, but most of the vertebra, like the ribs, are merely numbered ; among the arteries, the aorta only has a mononym ;

Source: wiktionary

Briefly, the adoption of calcar is a logical corollary of the recommendation which is common to the reports of all four American committees, vi., "Other things being equal, it is recommended that mononyms be preferred to polynyms." Calcar avis is a polyonym ; calcar is a mononym. If it be said that unguis is also a mononym, the answer is that in this case "other things" would not be equal, because (1) no general preference has ever been shown for it or for any term of which it is a constituent; (2) there would be lost the advantage of the correlation now existing between the ental ridge and the fissure collacated therewith.

Source: wiktionary

As the heroine, the tall, thin actress who calls itself Capucine is as crystalline and icy as her elegant mononym.

Source: wiktionary

The academic I already knew by reputation; they went by the mononym Farah and were one of the foremost authorities on Ilari poetry.

Source: wiktionary