faithful

Etymology

From Middle English feithful, equivalent to faith + -ful.

adj

1. Loyal; adhering firmly to person or cause.
   My dog is very faithful: he doesn't like to be petted by anybody else.
2. Having faith.
   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.
   My servant is very faithful.
4. Consistent with reality.
   I would consider that a very faithful reproduction.
5. Engaging in sexual relations only with one's spouse or long-term sexual partner.
   They had been faithful to each other all of their married life.
   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">representation or functors in category theory.

noun

1. (in the plural) The practicing members of a religion or followers of a cause.
   The faithful pray five times a day.
   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, →OCLC
2. Someone or something that is faithful or reliable.
   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. September 30, 2009, Bruce DeMara, “Shaw's comedy gets teeth”, in Toronto Star