Webster's Revised Unabridged Dictionary · 1913

Impalpable

Impalpable , adjective

[Prefix im- not + palpable: compare French impalpable.]

1.
Not palpable; that cannot be felt; extremely fine, so that no grit can be perceived by touch.
Impalpable powder. — Boyle
2.
Not material; intangible; incorporeal.
Impalpable, void, and bodiless. — Holland
3.
Not apprehensible, or readily apprehensible, by the mind; unreal; as, impalpable distinctions.