This is the 3832nd most frequent Korean word.
써온
"써온" means "have written" or "have used," depending on context.
Here, "써온" conveys the continuous action of writing a journal over a period of several years.
그는 여러 해 동안 한 권의 일기를 써온 사람입니다.
He is a person who has been writing a journal for many years.
In this sentence, "써온" indicates the accumulation of written works by her over time.
그녀가 써온 글들을 이제 출판하려고 합니다.
She is about to publish the writings she has been compiling.
"써온" here implies the consistent application or use of a method up to the present.