impalpable

梦境中的情感难以捉摸，醒来后便消散了。

The emotions in dreams are ___impalpable and fade upon waking.

她感到一种难以名状的焦虑，却无法指出其来源。

She felt an ___impalpable anxiety that she could not trace to any source.

经济复苏的迹象如此微弱，以至于几乎无法察觉。

The signs of economic recovery were so ___impalpable as to be almost imperceptible.