|(polite) older sister||oneesan|
|(polite) older brother||oniisan|
|(polite) younger sister||imoutosan|
|(polite) younger brother||otoutosan|
Notice that the first set of words has both a polite and a regular form. (The polite form is marked with (polite).) The polite form should be used when referring to others' families or when speaking to people in your own family. The other form should be used when referring to your family to members outside your family.