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

An inability of a person to sleep 

Insomnia

The most appropriate one-word substitution for "an inability of a person to sleep" is insomnia.

• Imbecile is a dated term for someone who is intellectually disabled.
• Anxious is someone who is worried or nervous.
• Insomnia is the inability to fall asleep or to stay asleep.
• Hypersomnia is the excessive need for sleep.

The word insomnia comes from the Latin words "in," meaning "not," and "somnus," meaning "sleep." Insomnia is a common sleep disorder that affects millions of people worldwide. It can be caused by a variety of factors, including stress, anxiety, depression, medical conditions, and medications.