The word "frenetical" is spelled with a "c" instead of a "z" because it is derived from the Greek word "phrenetikos," which was originally spelled with a "k." The "k" sound in IPA phonetic transcription is represented by "k," while the "t" sound is represented by "t." Therefore, the spelling "frenetical" accurately reflects the word's Greek origins and pronunciation. It is important to pay attention to the spelling of words, as it can greatly impact their meaning and interpretation.