Use fervor to describe an intensity of emotion or expression. Fans of the Los Angeles Dodgers show so much fervor that they "bleed Dodger blue."
This noun comes to us from Latin fervere, meaning "to boil, glow." In the English word fervor, the suffix –or means "a condition or property of something." There is another –or suffix that means "a person or thing that does the thing expressed by the verb." A corresponding adjective is fervent; synonyms of the noun and adjective are ardor and ardent.