(in the plural) The practicing members of a religion or followers of a cause.
The faithful pray five times a day.
Someone or something that is faithful or reliable.
Loyal; adhering firmly to person or cause.
My dog is a very faithful dog: he doesn't like to be petted by anybody else.
Having faith.
Reliable; worthy of trust.
My servant is very faithful.
Consistent with reality.
I would consider that a very faithful reproduction.
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.
(mathematics) Injective in specific contexts, e.g. of representations in representation or functors in category theory.