From Wiktionary, the free dictionary
chop mill (plural chop mills)
- (US) A mill in which grain is coarsely ground as feed for livestock.
- Synonym: chopping mill
1912 Dec, Modern Electrics, page 911/1:Mr. Stetzle sighed. "Gee, I wish I could get in on something like that. Running a chopmill is a mighty slow way to get rich."