noun, adverb
after this; from now on; hereafter
Refers to a point in time after the present or a specified reference point; often used in formal or written contexts.
以後、気をつけます。
I'll be careful from now on.
午後6時以後は電話に出られません。
I cannot answer the phone after 6 p.m.
noun, adverb
thereafter; since then; after that
Used after a specific event or time expression, especially after あれ, それ, or the -te form of a verb, to mean 'after that' or 'since then'.
彼は大学を卒業して以後、一度も会っていない。
I haven't seen him since he graduated from university.
あれ以後、彼から連絡がない。
I haven't heard from him since then.
Compound of 以 (i, 'from') and 後 (go, 'after'). The kanji 已 is an older variant of 以, now rarely used.