happening

Etymology 1

From Middle English *happenynge, *happnynge, equivalent to happen + -ing.

verb

1. present participle and gerund of happen
   From the ground, Colombo’s port does not look like much.[…] But viewed from high up in one of the growing number of skyscrapers in Sri Lanka’s capital, it is clear that something extraordinary is happening: China is creating a shipping hub just 200 miles from India’s southern tip. 2013-06-08, “The new masters and commanders”, in The Economist, volume 407, number 8839, page 52

adj

1. (slang, of a place) Busy, lively; vibrant, dynamic; fashionable.
   […]San Francisco is not exactly the most happening place, you know. 2005, Wendy Lawton, Less is More, page 13
   When the show ends, the circular, sunken floor is one of the more happening dance clubs in town. 2006, Eliot Greenspan, Neil E. Schlecht, Frommer's Cuba, page 165
   They're a little noisy if you open your balcony door but otherwise offer a glimpse of one of Disney World's more happening places. 2011, Bob Sehlinger, Menasha Ridge, Len Testa, The Unofficial Guide Walt Disney World 2012, page 157
2. (slang, of a person or product) Trendy, up-to-the-minute.
   Every show has its hottest, most happening trends. If I were to isolate just one for hardware and one for software, this year's hot hardware would be the 386 machines, and the happening software would be desktop publishing. November 16 1987, Steve Gibson, “Desktop Publishing, 386-Based Machines, ‘Happening’ Trends at Comdex”, in InfoWorld, page 42
   Going strong since 2006, this ephemeral nightclub (it's open only for 50 nights each year, in July and August) has become the hottest ticket in DJ land, a combination of the most happening names in music and its spectacular setting at the heart of the Palais des Festivals. 2009, Nicola Williams, Oliver Berry, Steve Fallon, France, Lonely Planet, page 883
   San Antonio is the newest, tiniest, and most “happening” wine appellation in Chile, with just four boutique wineries that focus on quality, not quantity, producing fine pinot noir, sauvignon blanc, and syrah. 2011, Nicholas Gill, Christie Pashby, Kristina Schreck, Frommer's Chile & Easter Island, unnumbered page

Etymology 2

From Middle English happenyng, equivalent to happen + -ing.

noun

1. Something that happens.
2. A spontaneous or improvised event, especially one that involves audience participation.