loon·y or loon·ey also lun·y (lnē) Informal
adj. loon·i·er, loon·i·est also lun·i·er or lun·i·est
1. Extremely foolish or silly.
2. Mentally deranged; crazy.
n. pl. loon·ies or loon·eys also lun·ies
A foolish or crazy person.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 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.