Concept:
One-word substitutions replace a group of words with a single word that conveys the same meaning, making language concise and effective.
Step 1: Understand the phrase.
"A person who speaks many languages" refers to someone fluent in multiple languages.
Step 2: Evaluate the options.
- Bilingual $\rightarrow$ speaks two languages (incorrect)
- Polyglot $\rightarrow$ speaks many languages (correct)
- Linguist $\rightarrow$ studies languages (incorrect)
- Orator $\rightarrow$ skilled speaker (incorrect)
Step 3: Conclusion.
Thus, the correct one-word substitution is "Polyglot".