1. take the plunge - Verb
2. take the plunge - Phrase
(idiomatic) To begin any major commitment.
(idiomatic) To get engaged to be married.
Source: en.wiktionary.orgI passed an entire night in mental turmoil. Ultimately, I decided to take the plunge without even informing my family. Gulzarilal Nanda
If you wait until the right time to have a child you'll die childless, and I think film making is very much the same thing. You just have to take the plunge and just start shooting something even if it's bad. James Cameron (director)
Keep only those things that speak to your heart. Then take the plunge and discard all the rest. By doing this, you can reset your life and embark on a new lifestyle. Marie Kondo
After you take the plunge and click "I Want One," do some math to figure out the total number of shirts you'll be ordering. Source: Internet
Fans were also given plenty of incentive to take the plunge as well; a mysterious underwater lab with a glass dome could be seen in the trailer, its depths waiting to be plumbed by intrepid divers. Source: Internet
As much as I would like to place the blame on my husband and a couple of fellow bloggers (Carl V and Heather) who encouraged me to take the plunge, in truth, it didn’t take much prodding at all. Source: Internet