Indeed there is no reason to speak of polyphenols, as the International Union of Chemistry decided :
Phenols : Compounds having one or more hydroxy groups attached to a benzene or other arene ring, e.g. 2-naphthol:
Source : PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1357
https://doi.org/10.1351/goldbook.P04539
From now on, I shall speak of phenols.
PS. By the way, tannins are very specific phenols.
