Promptliest is an adjective that means the quickest or most immediate. There are various synonyms for promptliest such as quick, rapid, speedy, swift, instant, punctual, expeditious, and fast. These words are often used to describe something that is done quickly or without delay. For instance, a promptliest response to an emergency situation can be the difference between life and death. In the business world, a prompt service is highly valued and can lead to repeat customers. In writing, using synonyms for promptliest can add variety to your language and help you to avoid repetitions.