late 12c., mēk, "gentle or mild of temper; forbearing under injury or annoyance; humble, unassuming;" of a woman, "modest," from a Scandinavian source such as Old Norse mjukr "soft, pliant, gentle," from Proto-Germanic *meukaz (source also of Gothic muka-modei "humility," Dutch muik "soft"), a word of uncertain origin, perhaps from PIE *meug- "slippery, slimy." In the Bible, it translates Latin mansuetus from Vulgate (for which see mansuetude). Sense of "submissive, obedient, docile" is from c. 1300.
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/meekness">Etymology of meekness by etymonline</a>
Harper, D. (n.d.). Etymology of meekness. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/meekness