theorem
Concise Oxford English Dictionary © 2008 Oxford University Press:
theorem /ˈθɪərəm/
▶noun Physics & Mathematics a general proposition not self-evident but proved by a chain of reasoning.
■ a rule in algebra or other branches of mathematics expressed by symbols or formulae.
– derivatives
theorematic /-ˈmatɪk/ adjective.
theorematic /-ˈmatɪk/ adjective.
– origin C16: from Fr. théorème, or via late L. from Gk theōrēma ‘speculation, proposition’.
'theorem' also found in these Oxford entries:

