from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A solid, toxic, selective herbicide, C9H7O3Cl3, used primarily against woody plants.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a herbicide that is effective in controlling woody plants but is toxic to animals
Probably Latin silva, forest + ex(terminator).(American Heritage® Dictionary of the English Language, Fourth Edition)