IPA: /ˌpɒlɪˈtoʊnəl/
KK: /ˈpɑlɪˌtoʊnəl/
Relating to or involving the use of multiple musical tonalities at the same time.
The composer created a polytonal piece that blended different musical keys.
Polytonal → It is formed from "poly-" (from Greek "polus", meaning many) and "tonal" (from Latin "tonalis", meaning relating to tone). The word "polytonal" refers to music that uses multiple tones or keys simultaneously.
Think of 'many' ('poly-') tones ('tonal') coming together in music — that's what polytonal means.