oc·ta·vo (ŏk-tāvō, -tä-)
n. pl. oc·ta·vos
1. The page size, from 5 by 8 inches to 6 by 9.5 inches, of a book composed of printer's sheets folded into eight leaves.
2. A book composed of octavo pages. In both senses also called eightvo.
[Medieval Latin (in) octāvō, (in) an eighth, from Latin, ablative sing. of octāvus, eighth, from octō, eight; see oktō(u) in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.