1. noun A hopelessly inept, blundering person who can't do anything right. That poor sad sack Sarah has been stuck in the same dead-end role in this company for years.

2. noun A sad, moping person, especially one who refuses to try and improve their mood or situation. Don't be such a sad sack—I know you're disappointed about missing the concert, but that doesn't mean we can't have fun tonight! He just sat there like a sad sack, sulking in the corner of the party.

3. verb To be in a sad, moping mood, especially while refusing to try and improve one's mood or situation. Usually used in the continuous tense; sometimes hyphenated. If you don't quit sad sacking back there, I'm going to turn the car around and drive us all straight back home! Bill's been sad-sacking around the office ever since he got passed over for the promotion.

1. To put or pack something into a sack or bag. In this usage, a noun or pronoun can be used between "sack" and "up." My first job was sacking up people's groceries at the store down the road for $5 an hour. Don't worry about wrinkling the clothes. Just sack them up.

2. vulgar slang To start acting in a strong, confident, and/or courageous manner, especially after having previously failed to do so. In this usage, "sack" is slang for the scrotum, a reference to testicles, which are used figuratively to represent confidence, courage, bravado, etc. The phrase is not exclusively applied to males. Often used as an imperative. You need to sack up and ask your boss for a raise already! What's he going to do, fire you? Janet, I know you're nervous about asking Tom out on a date, but just sack up and give it a shot!

3. slang To have sexual relations with someone. In this usage, "sack" is slang for a bed. A: "I heard that Tom has been sacking up with some 30-year-old accountant from his old law firm." B: "Wow, he hasn't even been divorced a month!" I can't believe you and your ex-boyfriend sacked up again.