Atheism

[I_am_not_mafia]

The 'ism' in atheism denotes a system.

http://www.dictionary.com/browse/-ism

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).

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Metabolism refers to a system...

Meaningless. Virtually everything that exists in the world is either a system or part of a system.