bygone
adj. C1 Advanced US //ˈbaɪˌɡɔn// UK //bˈaɪɡɒn// by·gone
adj. describing something that is no longer around or is in the past. You use it to talk about things that are old or have disappeared.
adj. relating to the past or having ceased to exist. Often used to describe a period or a way of life that is no longer current.
The old factory is a bygone era of heavy industry.
Walking through the old town, I felt like I was stepping into a bygone world of simpler times.
The bygone days of the gold rush have long since faded, replaced by a modern economy that relies on technology rather than manual labor.
From by (adverb) + gone.