Of, pertaining to, or of the nature of phenomena, or the appearances of things, as distinguished from the things in themselves; pertaining to the occurrences or changing phases of matter or mind.Of the nature of a phenomenon, or extraordinary fact in nature; so surprising or extraordinary as to arrest the attention or excite wonder; impressively notable or important; beyond what is common or usual; remarkable: as, the phenomenal growth of the United States; a brain of phenomenal size.n. That which is in the nature of a phenomenon.