faithful

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.”

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.”

6. Injective in specific contexts, e.g. of representations in representation or functors in category theory.
7. Of a module, whose annihilator is zero.

noun

1. (noun, plural)The practicing members of a religion or followers of a cause.

   “The faithful pray five times a day.”

   “The annual meeting was attended by the long-term party faithful.”

   “We Fremen have a saying: God created Arrakis to train the faithful. One cannot go against the word of God.”

   “In attacking a vital broadcaster, the US president is once again holding others to standards he flouts. But the Maga faithful might not let his links to the disgraced financier go[.]”

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.”