Lose is only a verb. To lose is to suffer a loss, to be deprived of, to part with, or to fail to keep possession of.
Loose is mainly an adjective used to describe things that are not tightly fitted. Where it is a verb, it means to release—for example, they loosed the dogs on the intruders—but the word is only rarely used this way. It also has a noun sense mainly confined to the idiom on the loose, which means at large. When you need a verb meaning to partially release or to relax, loosen is usually the best choice.
Lose four games in a row in the NFL and you’re pretty much finished. [Wall Street Journal]
Because I was so young and so skint I didn’t have much to lose when I first came to London. [Guardian]
If loose lending and over-borrowing didn’t cause the housing bubble, what did? [CNBC]
Just imagine what the company’s already cluttered competitive landscape would be like if HBO Go were loosed on the world as a standalone product? [Variety]
Attorneys have pressed that police should have alerted their force sooner to the possibility of a suspect on the loose marked with blood. [Roanoke Times]