What is "laustic"

"Laüstic", also known as "Le Rossignol", "Le Laustic", "Laostic", and "Aüstic", is a Breton lai by the medieval poet Marie de France. The title comes from the Breton word for " nightingale", a symbolic figure in the poem. It is the eighth poem in the collection known as the Lais of Marie de France, and the poem is only found in the manuscript known as Harley 978 (also called manuscript H). Like the other poems in the collection, Laüstic is written in the Anglo-Norman dialect of Old French, in couplets eight syllables long.