Antediluvian and Early

Antediluvian adjective - Dating or surviving from the distant past.

Early is a synonym for antediluvian in characteristic topic. In some cases you can use "Early" instead an adjective "Antediluvian", when it comes to topics like high, start, primeval, before the flood.

Early adjective - Relating to or occurring near the beginning of a process, series, or time period.

Antediluvian is a synonym for early in characteristic topic. You can use "Antediluvian" instead an adjective "Early", if it concerns topics such as high, start, primitive, primeval.