immemorial
adj. 远古的，古老的；无法追忆的
例句
It has remained virtually unchanged since time immemorial.
它几乎自古以来都维持不变。
《柯林斯英汉双解大词典》
From time immemorial man has approached woman with his proposal and has requested conjugality from her.
自古以来，男人就向女人求婚，并要求夫妇生活。
It's been like that since time immemorial.
自古以来就是这样。
