1540s, from Jew + -ish. Old English had Iudeisc; early Middle English used Judewish, Judeish (late 12c.). Similar formation in Dutch joodsch, Old High German judeisk, German jüdisch, Danish jödisk. Figurative use in reference to extortionate money-lending attested by c. 1600.
word-forming element denoting action, quality, or state, attached to an adjective or past participle to form an abstract noun, from Old English -nes(s), from Proto-Germanic *in-assu- (cognates: Old Saxon -nissi, Middle Dutch -nisse, Dutch -nis, Old High German -nissa, German -nis, Gothic -inassus), from *-in-, originally belonging to the noun stem, + *-assu-, abstract noun suffix, probably from the same root as Latin -tudo (see -tude).
<a href="https://www.etymonline.com/word/Jewishness">Etymology of Jewishness by etymonline</a>
Harper, D. (n.d.). Etymology of Jewishness. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/Jewishness