You'll need to carve out a definition of "viable" that excludes late term fetuses that could survive outside the womb but includes born babies that cannot survive without the care of adults.
Yeah I reject that definition and am not particularly considered with dictionary definitions when determining what is moral.
By this definition we couldn't consider any killing sanctioned by the state to be murder.
Sure, and your job is to argue that abortion causes the death of a viable human life.
Murder is defined as "the unlawful premeditated killing of one human being by another."
Abortion isn't that.