Merriam-Webster's Collegiate® Dictionary, 11th Edition
HAPPENING
I. noun
Date: 1551
something that happens ; occurrence , an event or series of events designed to evoke a spontaneous reaction to sensory, emotional, or spiritual stimuli, something (as an event) that is particularly interesting, entertaining, or important,
II. adjective
Date: 1977
very fashionable ; in , offering much stimulating activity