3. Characterized by refinement and niceness in drawing distinctions;
nicely discriminating; -- said of persons; as, a subtle logician;
refined; tenuous; sinuous; insinuating; hence, penetrative or
pervasive; -- said of the mind; its faculties, or its operations; as, a
subtle intellect; a subtle imagination; a subtle process of thought;
also, difficult of apprehension; elusive.
Things remote from use, obscure and subtle.
Milton.