Part-song for several voices without instrumental accompaniment

One word substitute is Madrigal.

Ballad: a poem or song narrating a story in short stanzas. Traditional ballads are typically of unknown authorship, having been passed on orally from one generation to the next.
Madrigal: a part-song for several voices, especially one of the Renaissance period, typically unaccompanied and arranged in elaborate counterpoint.
Panegyric: a public speech or published text in praise of someone or something.
Limerick: a humorous five-line poem with a rhyme scheme aabba.