Q: Should “soignée” and “trompe l’oeil” be underlined? Where can I obtain a list of foreign words (especially French) to be underlined and those to be left alone?
A: The Chicago Manual of Style (15th ed.) advises italicizing, not underlining, isolated foreign terms. But it recommends using italics only if the foreign terms “are likely to be unfamiliar to readers.” Otherwise, roman (that is, upright) type should be used.
How can you tell whether a foreign word or phrase is familiar or not? Consult a dictionary.
“Soigné” and “trompe l’oeil” are regular entries in both The American Heritage Dictionary of the English Language (4th ed.) and Merriam-Webster’s Collegiate Dictionary (11th ed.).
This indicates that the two terms have been adopted into English. Thus, they shouldn’t be italicized when used in an English sentence.
American Heritage lists only those foreign terms that have been adopted into English. Merriam-Webster’s lists both adopted foreign terms and the less familiar ones.
M-W includes adopted foreign terms in the main A-Z section, alongside other English words. It lists less familiar foreign terms – those not fully adopted into English – in a separate section at the back called “Foreign Words & Phrases.”
For example, M-W lists “enfant terrible” in the main section, but the less familiar “enfant chéri” in the back. This indicates that the first would not be italicized, while the second should be.
M-W explains: “Foreign words and phrases that have not been fully adopted into English are italicized. In general, any word that appears in the main A-Z vocabulary of this dictionary does not need to be italicized.” (Page 1613)