Q. Is Chanuka called a Yom Tov or Chag? When you write a Chanuka card can you mention that title?

A. Horav Shlomo Miller’s Shlit’a opinion is that it is called a Chag and a Yom Tov as we find in Shulchan Aruch (Y. D. 217: 47) regarding a neder done exempting those days, that Chanuka and Purim are also considered Yomim Tovim at least in name. Taz (ibid. 38) explains that in the language and expressions that people commonly use, the are included.
Orchos Rabeinu mentions that Horav Chaim Kanievsky zt’l would indeed greet people with a “Gut Yom Tov” on Chanuka. See similar opinion in Alenu Leshabeach (6: p. 100).

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a