noun, noun which may take the genitive case particle 'no'
ancient times; prehistoric times
Refers to the very distant past, often before recorded history. Used in historical, geological, or mythological contexts.
This fossil belongs to a prehistoric creature.
In ancient times, this area was covered by the sea.
太古の生物の化石が発見された。
Fossils of prehistoric creatures were discovered.
この伝説は太古から語り継がれてきた。
This legend has been passed down since prehistoric times.
大昔 is a casual, everyday way to say 'a long time ago', whereas 太古 is a more formal, literary term for the deep prehistoric past.
太古 emphasizes a vast, ancient span of time long past, while 原始 focuses on the primitive, undeveloped state of things from that time.
太古 refers to primeval or prehistoric times, an even more remote past than the nostalgic antiquity evoked by 古.
現代 means the modern, present era, directly contrasting with 太古's sense of the ancient, prehistoric past.
太鼓 (a drum) is pronounced identically to 太古 but has a completely unrelated meaning, so context is needed to distinguish them.
Composed of 太 (great, very) and 古 (old, ancient). The exact historical derivation is uncertain, but the combination naturally conveys 'great antiquity'.