Murder, because under the law the killing of an unborn child by a 2nd party without the mothers consent is illegal.
The killing of an unborn child with the consent of the mother that is within the legal parameters for abortions is legal and thus can not be murder.
As Rush states, words have meaning. The killing is no less gruesome by not being called murder. However, the fact is that abortion is not "murder"...at best it's "killing". Murder requires illegality