"Haddest being" is an archaic and rarely used phrase that means "you had been." As language has evolved over time, many words and phrases have fallen out of common use. Synonyms for "haddest being" include "were," "had been," "had existed," "had lived," and "had dwelt." These words can be used in place of "haddest being" to convey the same meaning in more modern language. It's important to keep in mind the context and intended audience when using archaic language or synonyms to ensure clear communication.