take the plunge
to decide to do something important or risky, especially after thinking about it for a long time

[TahlilGaran] Dictionary of Contemporary English ▲

take the plunge
to decide to do something.
Those women who took the plunge and ran for the state legislature enjoyed great success.

Usage notes: usually said about doing something that involves some risk

[TahlilGaran] English Idioms Dictionary ▲

take the plunge
to do something decisive (such as getting married)
My friend decided to take the plunge and will get married next year.

[TahlilGaran] English Idioms Dictionary ▲

take the plunge
v. phr. To take a fatal or decisive step; venture.
When I asked Don when he and Melissa were going to get married, he answered that they'll take the plunge in September.

[TahlilGaran] English Idioms Dictionary ▲