hold (one's) breath

1. To intentionally stop breathing for a short period of time. I can't hold my breath for very long, so I doubt I'll be able to swim down deep enough to grab the rings. I don't care how long you think you can hold your breath—you're not going back into a house with gas leak! She's been swimming for years, so she's pretty good at holding her breath.

2. To wait for something specific to happen. In this usage, the phrase is usually used in the negative. The electrician said he'd be here before noon, but I won't hold my breath. She wrote a letter of complaint to the airline asking for a refund, but she said she isn't holding her breath. You think Mom is going to let you go to a party the seniors are throwing? Ha, don't hold your breath.

hold one's breath

1. Be excited, anxious, or nervous. For example, The election was so close that I held my breath until the final results were in, or I'm holding my breath until every-one's been heard from. This expression alludes to the interruption of normal breathing; the literal usage dating from the early 1700s.

2. not hold one's breath. An expression used to mean one is not awaiting something, as in I'm hoping to hear if I got the job, but I'm not holding my breath. It often is put as an imperative, don't hold your breath, meaning "don't expect it, it's not likely," as in They may get married this summer, but don't hold your breath. This expression in effect implies it is unwise to stop breathing until a particular event occurs, since it may never come to pass. [Slang; mid-1900s]