The spelling of "wast foul mouthed" may seem confusing but it can be easily understood through its phonetic transcription /wɑːst faʊl maʊðd/. "Wast" is an archaic form of "was" commonly used in Shakespeare's plays. "Foul" is spelled with a silent "u" and pronounced /faʊl/, while "mouthed" is pronounced /maʊðd/. Together, the phrase means someone was vulgar and offensive in their speech or communication. It is important to understand the spelling and pronunciation of words, especially in writing, to effectively express ideas and communicate with others.