Giantish was a collection of related languages or dialects spoken by the Giants of Middle-Earth.The language originated in Aman and was believed by many Scholars to be related to Valarin, though the guttural giantish bore little obvious resemblance to it's supposed ancestor.
Speculations[]
Tolkien never seems to have devised a language for the giants.The few Giant names mentioned in his books, Gilim, Nan and Glend seem to be of Goldogrin origin while the name of the giant Tarlang might be either Sindarin or perhaps a sindarinized name of Old Gondorian origin.