Nouns with the suffix ‘er’ or ‘or’ When to add the suffix ‘er’ and when to add ‘or’ is a tricky question to answer. The suffixes ‘er’ and ‘or’ can be added to some verbs to make nouns that mean ‘a person or a thing that does something’. Unfortunately, there do not seem to be hard and fast rules about which to use; so you can have actor, accelerator and conqueror ending in ‘or’ but jeweller, foreigner and designer all end in ‘er’. Our latest set of pages is a great help in explaining this and familiarising children with the correct spelling of many of these nouns. Go to: English: Grammar: Prefixes and Suffixes