Trendy

HIP

It’s the opposite of square when describing someone who’s cool and up-to-date.

"Trendy" is a straightforward clue pointing to "HIP," a slang term for something fashionable or up-to-date. The word has been used since the mid-20th century to describe what’s currently popular, like music, style, or culture. Think of phrases like "hipster" or "get with the times"—it’s all about being in the know. No wordplay here, just a direct match for modern cool.