1. verb To blunder; to make a mistake or an error. I think I slipped up and sent the check to the wrong address. Wow, it looks like the accountants must have really slipped up this time.
2. verb To interfere with someone or their ability to do something; to cause someone to make a mistake or an error. In this usage, a noun or pronoun can be used between "slip" and "up." I have to concentrate while I do this, so please don't talk and slip me up! She always uses intimidation tactics to try to slip up her opponents.
3. noun A minor mistake, blunder, or mishandling. In this usage, the phrase is usually hyphenated. He's had one too many slip-ups in the office, so I think we have to let him go. He was overcharged due to a slip-up on our end.
See slip up