noun, used as a suffix
since; ever since
Attaches to a noun or time expression to mark the starting point of a continuing state or action. Often used in formal or written contexts.
先月以来、彼に会っていない。
I haven't seen him since last month.
卒業以来、故郷に帰
I haven't returned to my hometown since graduation.
noun, adverb
ever since; from that time on
Used adverbially or as a noun to refer to the entire period after a past event. Often appears as それ以来 or あれ以来.
彼は事故に遭って、それ以来ずっと入院している。
He had an accident and has been hospitalized ever since.
あれ以来、彼女から連絡がない。
I haven't heard from her since then.