Also, set upon. Attack or assail, as in The dog set at the postman, or The hyenas set upon the wounded lion. The first term dates from the early 1400s, the variant from the late 1300s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.