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

A period of time in the past that was idyllically happy and peaceful.

Halcyon

The most appropriate one-word substitution for the given group of words "A period of time in the past that was idyllically happy and peaceful" is "Halcyon."

Explanation of the options:

☀ Condominium: Condominium refers to a type of housing where individual units are owned by different individuals or entities. It does not relate to a period of time in the past that was idyllically happy and peaceful.

☀ Halcyon: Halcyon means a period of time characterized by tranquility, happiness, and prosperity. It is often used to describe a peaceful and carefree time in the past.

☀ Nostalgia: Nostalgia refers to a sentimental longing or affection for the past. While it may include a longing for a happy and peaceful time, it does not specifically convey the idea of an idyllically happy and peaceful period.

☀ Carnivorous: Carnivorous refers to an organism or plant that feeds on flesh or meat. It does not relate to a period of time in the past that was idyllically happy and peaceful.