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

A speech to oneself, alone 

Soliloquy

The most appropriate one-word substitution for the given group of words is soliloquy.

• Colloquial means informal or relaxed in style.
• Melancholy means sad or pensive.
• Dialogue means a conversation between two or more people.
• Soliloquy means a speech to oneself, alone.