The word "horseradish" is in parentheses after he he translates מרור as "bitter herbs", it seems to me that he's merely suggesting horseradish as an example of bitter herbs.
I somewhat remember that the ArtScroll Gemara translates Tamkha as "horseradish", without any note suggesting that this might be controversial. But I'm not sure of that.
I've see jars of grated horseradish (e.g. chrain) and on the label, in Hebrew in parenthesis, "chazeres". What is the source of that translation?
Ivrit. There is no question or controversy that chazeres in pre-modern Hebrew was a synonym for chassah, but Ivrit has decided that one word is enough for lettuce, and repurposed chazeres for something else.The identification of Tamcha with horseradish is historically inaccurate, but at least it has sources.
Chasa is Aramaic IIRC. Chazeres is the Hebrew equivalent.Shmooli