The synonyms ancient and obsolete are sometimes interchangeable, but ancient applies to occurrence, existence, or use in or survival from the distant past.

// ancient accounts of dragons

Some common synonyms of obsolete are ancient, antiquated, antique, archaic, old, and venerable. While all these words mean "having come into existence or use in the more or less distant past," obsolete may apply to something regarded as no longer acceptable or useful even though it is still in existence.

// a computer that makes earlier models obsolete

Although the words old and obsolete have much in common, old may apply to either actual or merely relative length of existence.

// old houses

// an old sweater of mine