Subtle

hårfin

(of an argument or concept, words, etc.: requiring one to distinguish between fine points, especially if it is difficult to do so; difficult to grasp; not easily understood or obvious)

subtil

(of an argument or concept, words, etc.: requiring one to distinguish between fine points, especially if it is difficult to do so; difficult to grasp; not easily understood or obvious)

subtil

(of a person or animal, or of an action or words: clever or skilful in a crafty or devious way (cognates) — see also cunning, sly, wily)