The spelling of the word "most rectal" is determined by the English language's phonetic system. In IPA phonetic transcription, the first syllable "most" is pronounced as /məʊst/ with a long vowel sound. The second syllable "rectal" is pronounced as /rɛktəl/ with a short "e" sound and a stress on the first syllable. Together, they form a compound word that describes something as being predominantly related to the rectum. It is important to spell words correctly to avoid confusion and miscommunication.