Yclept is another way of saying also known as or AKA. Its original meaning was “going by the name of” and as such was used, in England, by Victorian police forces if a criminal had more than one name. It was also used by the criminals themselves when they wished to confused members of the general public to whom it was virtually unknown. It can also be used to mean so-called, in the sense of a name given to someone or something that is
unfit for purpose. At one time it was believed that the word was related
kleptomaniac, that the person it was applied to would steal anything, even another name, however, the origins of Yclept go back to the mediaeval English word “geoclepod” which meant “who is called” or “whose name is”. It’s very rarely used now, but could be useful if you want to bring some
wiseass know-it-all down to earth, because you can bet they won’t know what it means.