| Eely |
| Shifty |
| Evasive |
| Baffling |
| Slippery |
| Mysterious |
| Hard to get |
| Hard to find |
| Hard to grasp |
| Hard to catch |
| Hard to define |
| Hard to pin down |
| Hard to describe |
| Hard to nail down |
| Difficult to find |
| Like a greased pig |
| Difficult to grasp |
| Difficult to catch |
| Difficult to recall |
| Close to unattainable |
| Continually slipping away |
| Hard to understand or identify |