1. To live with someone or stay at someone's house temporarily. We've been shacking up at my brother's place while our house is being renovated. Do you mind if I shack up with you for a while? My wife and I are going through a bit of a rough patch.

2. To be in a sexual relationship with someone; to live or reside with someone in a sexual relationship. A: "I haven't seen Beth in a while." B: "She's been shacking up with some hotshot lawyer she started dating a few weeks ago." My parents still disapprove of us shacking up together before we're married. They're a little old-fashioned that way.

1. Living or sharing accommodations with someone while having a (usually casual) sexual relationship with them. I haven't seen my sister in weeks. I hear she's shacked up with some guy from Oklahoma these days. I was shacked up for a while with a woman I met downtown, but I've been on my own for the last couple of months.

2. Temporarily sharing accommodations with someone. A: "Do you have a place to stay while you're in town for the wedding?" B: "Yeah, I'm shacked up with my brother and his fiancée for the weekend."