noun, adverb
thereafter; after that; since then
Formal/literary word used in writing or formal speech to mean 'after that event' or 'since then'. Not used in casual conversation.
彼は大学を卒業し、爾後、故郷に戻って教師になった。
He graduated from university, and thereafter returned to his hometown and became a teacher.
その事件の爾後、彼の態度は一変した。
After that incident, his attitude changed completely.
A Sino-Japanese compound of 爾 (ji, 'that') and 後 (go, 'after'). The kanji 爾 is rarely used in modern Japanese outside of this and a few other formal compounds.