This Instructional Activity is a part of the Lesson 13, Unit 2, Grade 7. The prefix deci- is used in the metric system of measurement in which its meaning is one-tenth of a unit. Discuss the meaning of the term decimal as it is derived from the Latin word decimus, meaning tenth. What is the meaning of tenth? Provide real-world examples where tenths are regularly used. If a unit has been divided into ten equal-sized pieces, then one-tenth is the value of one of those ten pieces.