The term 'trendy one' can be defined by two crossword solutions: SWINGER (7 letters) and HIPSTER (7 letters). A SWINGER is someone who participates in a form of non-monogamous sexual activity, typically involving more than two people. A HIPSTER is someone who follows the latest trends and fashions, often with an ironic or countercultural attitude. Both terms refer to people who are fashionable and up-to-date with the latest trends.