If you say something icily, or look at someone icily, you do it in an angry or very unfriendly way. The feeling is like ice: no warmth, no smile, a sharp distance. It is not about the weather, and it is not about real ice in a glass. You most often use it of a voice, a look, a smile that is not really kind, or a short answer that shuts someone out. It comes from icy + -ly. The word is at home in stories and in fairly careful English; in very casual talk people may just say coldly, or “in a cold voice”. For actual cold roads or air, you say it is icy, or it is freezing — not icily.