What is the origin of yclept?

The archaic English verb yclept is the past participle of the equally archaic verb clepe “to call, name.” This initial y- derives from Old English ġe-, a prefix used to mark past participles; while ge- eventually fell out of use in English, many other Germanic languages, such as Dutch and German, still use ge- and similar prefixes to mark past participles. Even though ge- and y- are no longer used in English verbs, the prefixes have lived on in secret as the a- in words such as afford, aswoon, aware, and even dialectal ascared. Yclept was first recorded in the first millennium AD.