Old English unfægr "unlovely, not beautiful, deformed, hideous, unlovable," from un- (1) "not" + fair (adj.). Similar formation in Old Norse ufagr, Gothic unfagrs. Meaning "wicked, evil, bad" is recorded from c. 1300. Sense of "not equitable, unjust" is first recorded 1713. Related: Unfairly.
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).
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Definitions of unfairness from WordNet
partiality that is not fair or equitable;
injustice by virtue of not conforming with rules or standards;