0 the sound that people often make when they pause in the middle of what they are saying or pause before they speak, often because they are deciding what to say: --
1 abbreviation for emergency room US --
2 abbreviation for Elizabeth Regina: Queen Elizabeth II --
3 added to some verbs to form nouns that refer to people or things that do that particular activity: --
4 added to the names of particular subjects to form nouns that refer to people who have knowledge about or are studying that subject: --
an astronomer (= a person who knows about/studies astronomy)
a philosopher (= a person who knows about/studies philosophy)
5 added to the names of particular places to form nouns referring to people who come from those places: --
a northerner (= a person who comes from the north)