Thereafter/ˌðerˈæftər/ Definition 1 of 1Pro Tip 1/3Sequential Events Use 'thereafter' to indicate the next event in a sequence, often in formal writing. The company was founded, and thereafter it expanded rapidly. Pro Tip 2/3Time Gap 'Thereafter' suggests a period has passed since the initial event, not immediately after. She graduated in 2010, and thereafter began her career. Pro Tip 3/3Formal Tone 'Thereafter' carries a formal tone. In casual conversation, 'after that' is more common. He gave a speech and, thereafter, answered questions.