Loose hemp or jute fiber, sometimes treated with tar, creosote, or asphalt, used chiefly for caulking seams in wooden ships and packing pipe joints.
[Middle English okom, from Old English ācumba; see gembh- 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.
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.