"Happenin" is a colloquialism that is used to describe something that is exciting, interesting, or occurring in a significant way. Some common synonyms for "happenin" include happening, going on, taking place, occurring, transpiring, unfolding, developing, transpiring, and unfolding. Other synonyms for "happenin" include exciting, lively, vibrant, active, spirited, dynamic, and animated. Using synonyms for "happenin" can help to add variety and color to your language, making your communication more engaging and interesting. Whether you're describing a party, a concert, or any other event, using these synonyms can help to convey the excitement and energy of the experience.