1. To let something go; to start something up. Often used as an imperative. OK, the rocket is ready to launch. Let that thing rip! I replaced the spark plug, so go ahead and let it rip so we can see if there's any difference. We've spent so long working on this ad campaign that I'm excited to finally let it rip.

2. To do something without inhibition or restraint, typically with great enthusiasm or force. Wow, did you see that kick? He really let it rip. When I'm writing a first draft, I like to just let it rip and not worry about typos or grammar.

1. To let out a wild, uncontrolled burst of anger or frustration. Wow, I've never seen Dave let rip into anyone like that. He's usually so mild mannered. I was expecting Mom to really let rip after she found out we'd broken the window, but she just sent us to our room.

2. To fart, especially noisily and indiscreetly. I can't believe you let rip in front of my parents like that. I was absolutely mortified.