Select the most appropriate one-word substitution for the given group of words. 

Killing of one's son or daughter.

Filicide

The most appropriate one-word substitution for the killing of one's son or daughter is filicide.

• Regicide is the killing of a king or queen.
• Lunatic is an old-fashioned term for a person who is mentally ill.
• Infanticide is the killing of a child younger than one year old.

The word filicide is derived from the Latin words filius, meaning "son", and filia, meaning "daughter". It is a relatively rare word, but it is the most specific term for the killing of one's own child.