THESAURUS
croon
anthem, ballad, carol, chant, chirp, chirrup, choir, chorus, descant, do-re-mi, hum, hymn, intonate, intone, lilt, minstrel, pipe, psalm, quaver, roulade, serenade, shake, sing, sing in chorus, sol-fa, solmizate, tremolo, trill, troll, tweedle, tweedledee, twit, twitter, vocalize, warble, whistle, yodel