The spelling of the word "haddest place" is based on Middle English, which had more inflectional endings than Modern English. In IPA phonetic transcription, it is /ˈhædɪst pleɪs/. "Haddest" is the second person singular past tense of "have," which was used to form the subjunctive mood. The "st" ending indicates that it is the second person singular form. "Place" is spelled as it is today, but the pronunciation may have been different in Middle English.
The phrase "haddest place" does not have a well-defined etymology as it is not a typical lexical item in English. "Haddest" is the archaic second person singular past tense form of the verb "to have" in Early Modern English. It was used to indicate possession or ownership, similar to "had" in modern English. However, "haddest place" does not have a universally recognized meaning or usage pattern in contemporary English.