Hilaire is the French form of Hilarius, a name of Latin and Greek origin meaning "cheerful". Derived from the Latin hilaris or the Greek ἱλαρός (hilaros), the name encapsulates a sense of joy and lightheartedness. Historically, it was borne by several saints, including the 4th-century theologian Saint Hilarius of Poitiers and a 5th-century pope, which contributed to its spread in Christian Europe.
In France, Hilaire has been in use since the Middle Ages, often given in honor of Saint Hilarius. The name has also functioned as a surname, with notable bearers like the French painter Hilaire-Germain-Edgar Degas and the author Hilaire Belloc. While its usage as a first name has declined in recent decades, it remains a classic in French onomastics.
The name has various cognates across European languages, such as Hilary in English, Ilari in Finnish, and Hillar in Estonian, reflecting its widespread adoption through Christian naming traditions.
Sources: Wikipedia — Hilaire