hy·per·bo·le 
(hī-pûrbə-lē)
(hī-pûrbə-lē)n.
A figure of speech in which exaggeration is used for emphasis or effect, as in I could sleep for a year or This book weighs a ton.
[Latin hyperbolē, from Greek huperbolē, excess, from huperballein, to exceed : huper, beyond; see HYPER- + ballein, to throw; see gwelə- in the Appendix of Indo-European roots.]