The adjective 'mean' (unkind, base) descends from Old English 'gemǣne' (common, shared), from Proto-Germanic *gamainiz and PIE *mey- (to exchange) — a classic case of pejoration, where 'common to all' gradually soured into 'low-born,' then 'base in character,' and finally 'cruel.'
Unkind, spiteful, or unfair; of low quality or social standing; lacking generosity; base or ignoble.
From Old English 'gemǣne' meaning 'common, shared, general, public,' from Proto-Germanic *gamainiz (shared, common, held in common), from PIE *mey- (to change, to exchange, to move). The semantic shift from 'common' to 'inferior' to 'unkind' is a textbook case of pejoration — a word's meaning deteriorating over centuries. What was once simply 'shared by all' became 'low-born' (because what is common is not aristocratic), then 'base in character' (because low birth implies low morals, in class-conscious thinking), and finally 'deliberately cruel or unkind' (the dominant modern American sense). The same root gives
The three English words spelled 'mean' — to intend (from PIE *mey-no-, to think), unkind/common (from PIE *mey-, to exchange), and average (from Latin medianus via French) — are three entirely separate etymologies that collided into one spelling by coincidence, making 'mean' one of English's most extreme homonyms.