This is the 17346th most frequent Korean word.
선생님이
"선생님이" means "teacher (subject marker)."
Here, '선생님이' is used to indicate the subject 'the teacher,' describing their characteristic of being kind.
선생님이 정말 친절하시네요.
The teacher is really kind.
'선생님이' in this sentence specifies the subject 'the teacher,' who was late to arrive at school.
선생님이 오늘 학교에 늦게 오셨어요.
The teacher arrived late at school today.
In this sentence, '선생님이' denotes the subject 'the teacher,' who is actively performing the action of teaching.