Hinduism is not exactly polytheistic, because the term ‘Hinduism’ itself is an arbitrarily constructed concept.
The Bhagavad-Gita, the main scripture of what we know today as Hinduism, is deeply monotheistic, and echoes that declaration throughout its length.
Nor is Hinduism exactly monotheistic. Would be an enjoyable discussion to follow should it come up elsewhere in a more suitable topic.
If Hinduism as practiced is not polytheistic, then the word has no meaning.