If you want to bug a Latin student, assign a passage that includes the word "cream." The Romans had no word for it, so your student will have to improvise some clumsy translation like "spuma lactis" (milk scum).
The fact is, the Greeks and Romans scarcely ever consumed milk in any form but cheese. Fresh milk spoils quickly unless pasteurized and refrigerated, especially in the warm Mediterranean climate. Even yogurt (oxygala) didn't keep well enough to be a significant part of their diet.
The word "butter" does come from Greek, where "boutyron" has the odd literal meaning "cow cheese," suggesting that the Greeks, who mostly herded sheep and goats, picked up the idea from some cattle-breeding neighbors of theirs. They certainly found the very idea of cooking with it terribly amusing, something only a wacky Thracian would do. In ancient Greece and Rome, you used olive oil for cooking; butter was for external application only--rubbing on a burn, for instance.
People obviously changed their minds during the Middle Ages, particularly in the former Roman colony of Gaul. In their cooler climate, the Celtic ancestors of the French may have had a word for cream, but the French didn't end up using a Celtic word. Instead, they adapted a word from the Mediterranean, "chrisma," which was the name of a mixture of olive oil and fragrant balsam used for another of those external uses, the religious ceremony of anointing.
It doesn't sound very culinary, but the French knew what they wanted and they didn't care where they got a word for it. As a result of their obsession, most European languages have adopted the French word "cre^me" in a culinary context, even if they have their own word for cream in the sense of that stuff you skim from whole milk.