adverb
Literary adverb used in formal or written contexts to refer to a point in the past from which something has continued or changed. In modern Japanese, それ以来 or その後 are more common.
彼は十年前に故郷を離れ、爾来一度も帰っていない。
He left his hometown ten years ago and has not returned since.
その事件の後、爾来彼女の態度は変わった。
After that incident, her attitude changed from then on.
Compound of 爾 (ji, 'that') and 来 (rai, 'coming'), literally 'from that coming'. The exact historical derivation is uncertain, but it has been used as a literary adverb since classical Japanese.