Hi, an objection is a protest against something, when someone does not agree. If you watch American tv shows set in court rooms, you will often see lawyers object to what the other side is saying. Rejection is similar, it is when you discard something you don't want, or someone even. You might hear people say they fear rejection if they approach someone they like. Hope this helps

The 'rejection"is used as noun,means "抛弃，被抛弃的东西......", and the'objection"is used as noun too,but it means "反对，异议........"