elusive
ih-LOO-sivadjMeaning hard to find, catch or remember
Memory hook e-LOOSE-ive: it gets LOOSE every time. Every time Pip swings his net, the butterfly slips loose and flutters just out of reach; it is elusive.
The elusive snow leopard is rarely caught on camera.
In context The answer stayed elusive: every time Maya thought she had remembered the word, it slipped away again like a fish between her fingers.
Similar slippery, evasive, fleeting, hard to pin down
Opposite accessible, obtainable
From Latin eludere, “to escape by a trick”: e- (out) + ludere (to play).