suffix indicating state, condition, or quality; also activity or the result of it (as in victory, history, etc.), via Anglo-French and Old French -é, from Latin -ia, Greek -ia, from PIE *-a-, suffix forming abstract or collective nouns. It is etymologically identical with -ia and the second element in -cy, -ery, -logy, etc.
Among hundreds of Middle English words it formed are yfallen, yhacked ("completely hacked," probably now again useful), yknow, ymarried, ywrought.
a late-developing letter in English. Called ipsilon in German, upsilon in Greek, the English name is of obscure origin. The sound at the beginning of yard, yes, yield, etc. is from Old English words with initial g- as in got and y- as in yet, which were considered the same sound and often transcribed as Ȝ, known as yogh. The system was altered by French scribes, who brought over the continental use of -g- and from the early 1200s used -y- and sometimes -gh- to replace Ȝ. The French also tended to substitute -y- for -i-, especially before -u-, -n-, or -m-, or at the end of words, to avoid confusion in reading (see U), might also partly explain this tendency in Middle English. As short for YMCA, etc., by 1915.