1. pl. lice (līs) Any of numerous small, flat-bodied, wingless biting or sucking insects of the order Phthiraptera, which live as external parasites on birds and mammals, including humans. The lice are sometimes classified together with the psocids in the order Psocodea.
2. pl. lous·es (lousĭz) Slang A mean or despicable person.
tr.v. loused, lous·ing, lous·es
To bungle. Often used with up: louse up a deal.
[Middle English, from Old English lūs; see lūs- in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 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.