The antonyms of the phrase "concrete happening" would refer to events that are abstract, intangible or uncertain. Some of the antonyms for "concrete happening" include things like possibilities, speculations, uncertainties, and conjectures. Such events are often subjective and difficult to pin down, leaving room for interpretation or debate. Other antonyms that might be used to describe events that are less concrete include concepts such as abstract ideas, theoretical concepts, potential occurrences, or hypothetical scenarios. Overall, the antonyms for "concrete happening" denote the kinds of events or ideas that are more open-ended, ambiguous or imprecise, and which lack the concrete evidence or tangible results that are characteristic of more concrete events.