Nouns ending in -er, -or, and -ar | Lexico.com
https://www.lexico.com/grammar/nouns-ending-in-er-or-and-arNouns ending in -er, -or, and -ar. Nouns ending in -er. This ending is the most common. It's usually added to verbs to make nouns with the meaning ‘a person or thing that does something’, for example: builder, farmer, sprinkler, or beeper. The -er ending can also be used to form nouns meaning: ‘a person or thing that has a particular quality or form’, for example:double-decker, …