tu·mor (tmər, ty-)
1. An abnormal growth of tissue resulting from uncontrolled, progressive multiplication of cells and serving no physiological function; a neoplasm.
2. A swollen part; a swelling: a plant tumor.
[Middle English tumour, from Latin tumor, from tumēre, to swell; see teuə- in the Appendix of Indo-European roots.]
tumor·al, tumor·ous adj.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
The American Heritage Dictionary Blog
Check out our blog, updated regularly, for new words and revised definitions, interesting images from the 5th edition, discussions of usage, and more.