polystylism
A musicological term referring to the use of multiple styles or techniques within a single composition, especially associated with 20th-century composers like Alfred Schnittke.
Schnittke is regarded as a representative composer of polystylism.
Compound of 多様 (tayō, 'diverse') + 式 (shiki, 'style') + 主義 (shugi, '-ism'). Likely a calque of English 'polystylism' or Russian 'полистилистика'.