a prefix occurring in certain obsolete words (ywis) and especially in archaic past participles: yclad.
Also i-.

Origin of y-

Middle English y-, i- (reduced variant a-), Old English ge-, prefix with perfective, intensifying, or collective force; cognate with Old Frisian, Old Saxon ge-, gi-, Gothic ga-, German ge-; compare perhaps Latin com- com-
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Word Origin and History for y-


perfective prefix, in y-clept, etc.; a deliberate archaism, introduced by Spenser and his imitators, representing an authentic Middle English prefix, from Old English ge-, originally meaning "with, together" but later a completive or perfective element, from Proto-Germanic *ga-. It is still living in German and Dutch ge-, and survives, disguised, in some English words (e.g. alike, aware, handiwork).

Online Etymology Dictionary, © 2010 Douglas Harper