"Ostentatious'' means characterized by vulgar or pretentious display — designed to impress or attract notice.
Step 1: Consider the meanings:
- "Showy'': Means flashy or trying to attract attention — matches "ostentatious''.
- "Modest'': Humble or restrained — opposite in meaning.
- "Ambiguous'': Unclear or having more than one meaning — unrelated.
- "Selfish'': Concerned with oneself — different concept entirely.
Hence, the correct synonym is "showy".