Plural of filth; multiple instances of dirt, refuse, or morally corrupt things.
From filth (Old English fylþ, meaning dirt, impurity, or moral corruption) + -s (regular plural marker). Filth comes from Germanic roots related to decay and corruption.
Most nouns in English just add -s or -es for plurals, but this wasn't always so simple—Old English had different plural forms for different noun classes. The modern -s system won out because it's simple and regular.
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