singleten, n. — Green’s Dictionary of Slang

singleten n.

also singleton

[? SE single, simple or as an elision of a single ten; the ten in cards ranks one below the knave, ‘he’ must therefore be a fool]

a very foolish person.

c.1698		B.E. Dict. Canting Crew n.p.: Single-ten, a very foolish, silly Fellow.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Singleten. A very foolish fellow.
1811		Lex. Balatronicum n.p.: singleton A very foolish fellow.