apostle

Concise Oxford English Dictionary © 2008 Oxford University Press:
apostle/əˈpɒsl/

▶noun

• 1 (Apostle) each of the twelve chief disciples of Jesus Christ.

  ■ an important early Christian teacher or missionary.

• 2 a vigorous and pioneering supporter of an idea or cause.

– derivatives
apostleship noun.

– origin OE apostol, via eccles. L. from Gk apostolos ‘messenger’, from apostellein ‘send forth’.