Mantra /mæntrə/ noun 

Definition:  Mantra is a motivating phrase or chant that is repeated over and over again. To the practitioners, the term, word, or phrase is believed to have some religious, spiritual, or magical powers. It helps to instill a sense of confidence or strength in the believer.

Etymology: The word comes from a Sanskrit word that means “spell, sacred message, counsel, or charm. It is usually used to echo one’s basic intimate principles.

In a Sentence

As the small actor struggled with the gigantic animal, he kept repeating the mantra, “everything is possible. Everything is possible.”

John repeats the mantra of a successful day every morning.

Before the engineers begin working, they always remind each other about their mantra—safety first.

Synonyms 

Intonation, Hymn, Chant

Antonyms 

Hypotonia, Keep Quiet