Decade/ˈdekeɪd/ Definition 1 of 4Pro Tip 1/3Measuring Time Use 'decade' to mark significant time periods in history or someone's life. The technological advances this last decade have been remarkable. Pro Tip 2/3Not Always Exact 'Decade' may refer to an approximate span of ten years, not exactly ten. The band's music shaped a generation, roughly a decade of influence. Pro Tip 3/3Cultural Milestones Use 'decade' when discussing periods known for specific cultural trends. The fashion trends of the 80s decade were truly unique.