Elusive

Hard to find, catch, or understand. It can describe physical things, like animals, or abstract things, like ideas or answers.

From Latin 'elusivus' meaning 'tending to elude,' from 'eludere' (to escape from, avoid), from 'e-' (out) + 'ludere' (to play). The original sense was like 'playing away' or dodging. English kept the idea of something always slipping out of your grasp.