“Seonsaengnim” (선생님) — teacher, doctor, lawyer, stranger
The hanja read as “born before”, which is why the word travels so far outside classrooms. If you do not know what to call someone older, this is the answer.
titles
“-ssi” and “-nim” (씨 · 님) — the suffix that sets your rank
Every textbook teaches 씨 as “the polite one”. Attach it to a surname alone, or to anyone senior to you, and it is the opposite of polite.