Sentence:  POLY′MYTHY (S[ubstantive]) in Poetry, a fault in an epic poem, when inſtead of a ſingle <WSD>mythos</WSD>, or fable, there is a multiplicity of them. 
Meaning of the word marked with <WSD> tags:  Anything transmitted by word of mouth, such as a fable, legend, narrative, story, or tale ("especially" a poetic tale).