To make free or give up control of something or someone; to release or discharge something or someone, as from confinement. Due to a lack of evidence, the suspects were let loose by police. Samantha was suspended for letting mice loose throughout the school.

To pass gas through one's anus; to fart. It smells like someone let one loose in the elevator when I walked in. Gross! Don't go letting one loose at the dinner table like that, Tom!