Whilom is an archaic word that means "formerly or once upon a time". Although it is rarely used in modern day English, it has a poetic ring to it that conjures up images of a bygone era. If you're looking for synonyms for whilom, you could use words like "erstwhile", "past", "previously", "formerly", "once", "one-time", "anciently", "old", "antecedent", "ex-" or "retired". These synonyms provide a variety of ways to describe something that happened in the past, allowing writers to create a sense of nostalgia or history in their works.