jump in

Etymology
For the US slang sense, compare.

Verb

 * 1) To enter something quickly, usually a mode of transport.
 * 2) To join in on an activity quickly.
 * 3) To interrupt someone while they are speaking.
 * 4)  To initiate into an organization, usually a gang, with violence.
 * 1)  To initiate into an organization, usually a gang, with violence.