from Wiktionary, Creative Commons Attribution/Share-Alike License
- v. To take hold of or mark with the thumbs; soil or mark with frequent thumbing.
from the GNU version of the Collaborative International Dictionary of English
- transitive v. To handle; to wear or soil by handling; as books.
from The Century Dictionary and Cyclopedia
- To soil or mark with frequent thumbing, as in turning the leaves of a much-read or much-studied book.
From be- + thumb. (Wiktionary)