adjective

resulting from or showing sincere and intense conviction.

an earnest student

serious,serious-minded,solemn,grave,sober,humourless,staid,steady,intense,committed,dedicated,assiduous,keen,diligent,zealous,industrious,hard-working,studious,thoughtful,cerebral,deep,profound,bookish,donnish,devout,heartfelt,wholehearted,sincere,impassioned,deeply felt,from the heart,full-hearted,fervent,fervid,ardent,passionate,burning,urgent,passional,perfervid