Treble/ˈtrebl/ Definition 1 of 4Pro Tip 1/2Math Multiplication Think of 'treble' as multiplying by three. It's used for quantities, not quality. If you buy one, you get two free – that's a treble offer! Pro Tip 2/2Not Always Negative 'Treble' can imply increase or improvement, not just excess or burden. Her happiness trebled when she heard the good news.