1
general::
1. At large free, as in That dog of theirs is on the loose all the time. [Second half of 1800s] 2. Acting without restraint, as in After the game the players were in town, on the loose. [Mid-1700s]
American Heritage Idioms
2
general::
Phrase(s): on the loose
running around free. • Look out! There is a bear on the loose from the zoo. • Most kids enjoy being on the loose when they go to college.
McGrawhill's American Idioms And Phrasal Verbs