-ism

1.
a suffix appearing in loanwords from Greek, where it was used to form action nouns from verbs (baptism); on this model, used as a productive suffix in the formation of nouns denoting action or practice, state or condition, principles, doctrines, a usage or characteristic, devotion or adherence, etc. (criticism; barbarism; Darwinism; despotism; plagiarism; realism; witticism; intellectualism).
Compare -ist, -ize.
Origin
< Greek -ismos, -isma noun suffixes, often directly, often through Latin -ismus, -isma, sometimes through French -isme, German -ismus (all ultimately < Gk)
British Dictionary definitions for -ism

-ism

suffix
1.
indicating an action, process, or result: criticism, terrorism
2.
indicating a state or condition: paganism
3.
indicating a doctrine, system, or body of principles and practices: Leninism, spiritualism
4.
indicating behaviour or a characteristic quality: heroism
5.
indicating a characteristic usage, esp of a language: colloquialism, Scotticism
6.
indicating prejudice on the basis specified: sexism, ageism
Word Origin
from Old French -isme, from Latin -ismus, from Greek -ismos
Word Origin and History for -ism

suffix forming nouns of action, state, condition, doctrine, from French -isme or directly from Latin -isma, -ismus, from Greek -isma, from stem of verbs in -izein. Used as an independent word, chiefly disparagingly, from 1670s.

-ism in Medicine

-ism suff.

  1. Action, process; practice: vegetarianism.

  2. Characteristic behavior or quality: puerilism.

  3. State; condition; quality: senilism.

  4. State or condition resulting from an excess of something specified: strychninism.

  5. Doctrine; theory; system of principles: Darwinism.