Definition of "faithful"

faithful

/ˈfeɪθ.fəl/

adjective
comparative more faithful, superlative most faithful
1. Loyal; adhering firmly to person or cause.
2. Having faith.
  Quotations
  The application of the old discipline, say the conservatives, would probably produce a smaller but more faithful Church.
  2009, Paul Lakeland, Church: Living Communion, page 162
3. Reliable; worthy of trust.
4. Consistent with reality.
5. Engaging in sexual relations only with one's spouse or long-term sexual partner.
  Quotations
  She wanted to be free to explore casual affairs, but her man had to be faithful.
  1976, The Missouri Breaks
6. (mathematics) Injective in specific contexts, e.g. of representations in representation or functors in category theory.
noun
plural faithfuls
1. (in the plural) The practicing members of a religion or followers of a cause.
  Quotations
  We Fremen have a saying: God created Arrakis to train the faithful. One cannot go against the word of God.
  1984, 2:11:25 from the start, in Dune‎ (Science Fiction), spoken by Paul Atreides
2. Someone or something that is faithful or reliable.
  Quotations
  Earlier this year, as the recession put a damper on ticket sales, Maxwell said the easy route would have been to go for the tried-and-true old faithfuls.
  2009 September 30, Bruce DeMara, “Shaw's comedy gets teeth”, in Toronto Star‎