The correct answer is (A) To smother or suffocate; to cause to die or lose consciousness by impairing normal breathing, as by gas or other noxious agents; to cause asphyxia.

Asphyxiate comes from Greek asphyxia + ate. Greek a- (without) and sphuxis (pulsation).

Examples of use:

• The murderer used a pillow to asphyxiate her.
• The coroner advised that the victim had been asphyxiated.