The term "past use" can be replaced with different synonyms that can come in handy in various contexts. "Former use" is a common replacement for "past use" that is often used to refer to something that was used previously but is no longer in use. Another possible synonym is "obsolete use," which implies that the use was outdated and replaced with a more modern alternative. "Historical use" is also a possible replacement that suggests a reference to the past that can be studied or learned from. Lastly, "defunct use" is another possible synonym that implies the use was no longer operational or functional.