odd-one-out
"Gloomy" describes a dark, sad, or depressing mood, placing it squarely opposite to "happy," which is why it doesn't belong grouped with words describing cheerfulness. Grouping by emotional tone rather than just dictionary meaning helps reveal which words actually share a mood.
"Joyful" and "cheerful" both describe positive, upbeat feelings closely aligned with "happy," making them the words that do belong in the group, since all three share the same warm emotional register.
This kind of odd-one-out exercise trains a subtler skill than simple definitions — recognizing connotation and mood, which matters enormously for sounding natural rather than just grammatically correct in English.
Quration — Quration English