means The quality or state of being the same — identical, unchanging, or monotonously alike across things or over time.

from Built from "same" plus the noun-making suffix "-ness." "Same" comes from Old Norse "samr" (the same), a word that planted itself in English and pushed aside an older native form, related to a deep Germanic and Indo-European root for "together, alike" — the same family that gives us "similar," "assemble," and the Greek-flavored "homo-." The "-ness" suffix, an old English workhorse, simply turns the adjective into a thing: same-state, the condition of being same.