Native SAE-speaker here, studied linguistics in undergrad, and "least common denominator" is a perfectly normal construction. The web isn't a perfect corpus, a

Native SAE-speaker here, studied linguistics in undergrad, and "least common denominator" is a perfectly normal construction. The web isn't a perfect corpus, and Google isn't a perfect corpus analysis tool, but with those caveats... Google results for "least common denominator": 738,000 / Google results for "most common denominator": 656,000 Additionally, as you point out, Wikipedia lists both as synonyms. Your original comment was correct and idiomatic English.