The word "Costlewe" is a rare, archaic word that is not commonly used in modern English. It is spelled phonetically as [ˈkɒsliːw]. The first syllable, "cos," is pronounced like "cause" without the "e" sound. The second syllable, "tle," is pronounced like "tul" with a subtle "eh" sound. The final syllable, "we," is pronounced like "wee." The spelling of the word seems unusual, perhaps influenced by Old or Middle English, but it is consistent with the phonetic rules of English.