adverb, noun which may take the genitive case particle 'no', noun
from ancient times; since olden days; from time immemorial
Used to describe something that has continued or been known since long ago. Often appears in formal, historical, or literary contexts, and can modify nouns with の or function adverbially.
Since ancient times, festivals have been held in this region.
We continue to preserve traditions from time immemorial.
Rice farming has been practiced in this region since ancient times.
This mountain has been regarded as a sacred place since ancient times.
This technique has been passed down in this village since ancient times.
古来 refers to continuity from ancient times, whereas 元来 means 'originally' or 'from the outset', focusing on origin rather than historical duration.
古来 emphasizes an extremely long, ancient history, whereas 旧来 just means something has continued for a long time without implying antiquity.
古来 is an adverb meaning 'since ancient times', while 古代 is a noun referring to 'ancient times/antiquity' itself, so they cannot be swapped grammatically.
Compound of 古 (old, ancient) and 来 (come, since). The exact historical derivation is uncertain, but the combination has been used to mean 'since ancient times' for centuries.