Select the option that can be used as a one-word substitute for the given phrase.

A public speech or piece of writing that expresses high praise or warm tribute to a person.

The correct option is Encomium.

Understanding the Given Phrase:
The phrase asks for a single word that means "a public speech or piece of writing that expresses high praise or warm tribute to a person."

Detailed Breakdown of Options:
• Encomium: A formal expression of high praise or a tribute delivered publicly through speech or writing. This perfectly matches the given definition.
• Sermon: A religious discourse or speech delivered by a member of the clergy, typically during a worship service, focused on scriptural or moral topics.
• Soliloquy: A speech given by a character in a play who is alone on stage, revealing their inner thoughts and feelings aloud to the audience.
• Elegy: A poem of serious reflection, usually written to express grief or lamentation for a person who has passed away.

Therefore, the correct one-word substitute is Encomium.