It comes from the Latin verb "jacere", which means "to throw" or "to cast". This root is used in many English words related to throwing, projecting, or casting:
* Eject: to throw out
* Inject: to throw in
* Project: to throw forward
* Projectile: something that is thrown
* Subject: something thrown under someone's control
* Reject: to throw back
Let me know if you'd like more examples!