The difference between Faithful and Untrustworthy

When used as adjectives, faithful means loyal, whereas untrustworthy means not deserving of trust.

Faithful is also noun with the meaning: the practicing members of a religion or followers of a cause.

check bellow for the other definitions of Faithful and Untrustworthy

Faithful as an adjective:

Loyal; adhering firmly to person or cause.

Examples:

"My dog is a very faithful dog: he doesn't like to be petted by anybody else."
Faithful as an adjective:

Having faith.
Faithful as an adjective:

Reliable; worthy of trust.

Examples:

"My servant is very faithful."
Faithful as an adjective:

Consistent with reality.

Examples:

"I would consider that a very faithful reproduction."
Faithful as an adjective:

Engaging in sexual relations only with one's spouse or long-term sexual partner.

Examples:

"They had been faithful to each other all of their married life."
Faithful as an adjective:

(mathematics) Injective in specific contexts, e.g. of representations in representation or functors in category theory.

Faithful as a noun (in the plural):

The practicing members of a religion or followers of a cause.

Examples:

"The faithful pray five times a day."
Faithful as a noun:

Someone or something that is faithful or reliable.