fervent
adj.adj. having or showing very strong and sincere feelings about something. You use this to describe someone who is extremely excited or serious about a belief or activity.
adj. characterised by intense emotion or strong belief; displaying great warmth or intensity of spirit.
She is a fervent supporter of the local football team.
The politician's speech was met with fervent applause from the crowd of loyal followers.
Despite the overwhelming evidence against his theory, the scientist remained a fervent believer in the existence of extraterrestrial life.
From Middle English fervent, from Old French fervent, from Latin fervens, ferventem, present participle of fervere (“to boil, ferment, glow, rage”).
Often used to modify nouns related to belief, support, or prayer.