This is the 2083rd most frequent Japanese word.
古
"Ancient" or "old."
The word '古い' is used here as an adjective to describe something as old, referring to the passage of time and the object's age.
この本はとても古いです。
This book is very old.
In this sentence, '古い' modifies '記憶' (memories), emphasizing their nature as belonging to the past.
古い記憶を思い出す。
I recall old memories.
Here, '古文' combines '古' (ancient) with '文' (text), representing classical literature in its collective form, which is commonly studied in historical contexts.