Things that are elusive are hard to find, pin down, or remember. They slip right out of your grasp.
Ever try to catch a mouse? It's not easy, because mice are quick and elusive — they're tough to catch. Rabbits are speedy, so they're elusive too. Also, things that are tough to understand or describe are elusive — like the concepts of love and beauty. If you had an idea and then forgot it, the idea is elusive: it slipped away. Anything you can't get hold of, with your hands or with your brain, is elusive.
Close your vocabulary gaps with personalized learning that focuses on teaching the words you need to know.