Q. Is it “ice-cream sandwich” or “ice cream sandwich”?
A. Let’s first consult Merriam-Webster. There you will find two forms of the compound. The first is an entry for hyphenated “ice-cream,” defined as an adjective meaning “of a color similar to that of vanilla ice cream.” The second is for unhyphenated “ice cream,” the far more popular noun form that you can eat. Now let’s consult the hyphenation table (CMOS 7.89). According to section 2, “noun + noun, single function (first noun modifies second noun),” you would add a hyphen before another noun (“ice-cream sandwich”). But we don’t need the hyphenation table in this case; as we have seen, “ice cream” is an established open compound (or a permanent compound, according to CMOS 7.82). And according to a Google Ngram query, the unhyphenated version is significantly more common in published books. For that matter, the hyphenated variety would be difficult to find on store shelves. (Our preference is for the classic sandwich featuring vanilla ice cream between two chocolate-flavored wafers—whatever the brand.) So “ice cream sandwich” is arguably the better choice.