The suffix ER in words such as painter, teacher, starter, and thinker generally indicates a person or thing that performs a particular action or has a specific quality. In this case, the suffix ER refers to a person or thing that does the action or has the quality related to the root word. For example, a painter is someone who paints, a teacher is someone who teaches, a starter is something that starts, and a thinker is someone who thinks.
