"character or state of being slight; smallness or lack of substance," c. 1600; see slight (adj.) + -ness.
Entries linking to slightness
slight adj.
early 14c., "flat, smooth, sleek; hairless," originally northern according to OED and probably from a Scandinavian source akin to Old Norse slettr "smooth, sleek," from Proto-Germanic *slikhtaz "slippery; flat, level, plain" (source also of Old Saxon slicht; Old Frisian sliucht, Low German slicht "smooth, plain common;" Old English -sliht "level," attested in eorðslihtes "level with the ground;" Old Frisian sliucht "smooth, slight," Middle Dutch sleht "even, plain," Old High German sleht, Gothic slaihts "smooth"), probably from a collateral form of PIE *sleig- "to smooth, glide, be muddy," from root *(s)lei- "slimy" (see slime (n.), and compare slick (v.)).
The original sense is obsolete. The evolution probably is from "smooth" (c. 1300), to "slim, slender; of light texture," hence "not good or strong; insubstantial, trifling, inferior, insignificant" (early 14c.). The meaning "small in amount" is from 1520s.
The sense of German cognate schlecht developed from "smooth, plain, simple" to "bad, mean, base," and as it did it was replaced in the original senses by schlicht, a back-formation from schlichten "to smooth, to plane," a derivative of schlecht in the old sense [Klein]. English slight also had the same tendency, and 15c.-17c., used of persons, could mean "humble, low; of little worth or account."
-ness
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).