In all instances, 'logue' means words/saying. 'Pro' means before, 'mono' means one or alone, 'epi' means in addition to, and 'dia' means across or between.
Explanation:
The prefixes of the words above refer to different positions in written or oral speech.
A Prologue usually prefaces a book: it introduces or comes before the actual writing.
An Epilogue usually comes at the end of a book: it serves as a conclusion or commentary in addition to the book.
A Monologue is a speech: one person speaking alone either in a play or in a conversation.
A Dialogue is a conversation: two or more people speaking between or among themselves.
