We claim the ornamental design for a defibrillator, substantially as shown and described.
FIG. 1 is a perspective view of a defibrillator showing our new design.
FIG. 2 is a top view thereof.
FIG. 3 is a bottom view thereof.
FIG. 4 is a front view thereof.
FIG. 5 is a back view thereof.
FIG. 6 is a left side view thereof.
FIG. 7 is a right side view thereof; and,
FIG. 8 is a second perspective view thereof.
The broken lines immediately adjacent the claimed subject matter represent the bounds of the claim, while all other broken lines are directed to environment and are for illustrative purposes only; the broken lines form no part of the claimed design.