Verb
To enter something quickly, usually a mode of transport.
I jumped in the car, and we sped off to the meeting.
To join in on an activity quickly.
To interrupt someone while they are speaking.
(US slang) To initiate into an organization, usually a gang, with violence.
Source: en.wiktionary.orgSo I am just sitting and waiting, listening, and if something exciting comes, I just jump in. George Gamow
To do anything truly worth doing, I must not stand back shivering and thinking of the cold and danger, but jump in with gusto and scramble through as well as I can. Og Mandino
Jump in a hole without looking, and there'll be a snake in it every time. Robert Jordan
Only a fool tries to jump in the fire. Kiganda Proverb
The frog does not jump in the daytime without reason. Nigerian Proverb
Why jump in the water before the ship turns over. Chinese Proverb