The phrase "wast the head of" is an archaic form of English that is no longer in common use. The spelling "wast" is the second person singular past tense of the verb "to be," as in "thou wast" meaning "you were." The pronunciation is [wɑːst], with the "a" sound represented by the IPA symbol "ɑː" and the "s" sound at the end of the word being silent. Overall, the spelling and pronunciation of "wast the head of" are indicative of the evolution of English language over time.