H-Hour is a military term used to describe the specific hour and time when a military operation is intended to begin. Synonyms for H-Hour include the words D-Day, T-Time, and kick-off. These words share similar connotations and are often used interchangeably. The term D-Day specifically refers to the day in which a military operation begins, but is often used to describe the precise moment as well. T-Time is another term used by military forces and stands for the exact time when an operation is scheduled to begin. Finally, kick-off is a more colloquial synonym for H-Hour and is commonly used in sports and games as well to describe the start of a match or event.