The word originates from the Latin name Valentinus, a derivative of valens meaning "strong, vigorous, healthy." This name was borne by several early Christian saints, most notably one martyred on February 14th. The association with romantic love arose in the late Middle Ages, likely influenced by the belief that birds began their mating season on that date. The modern senses of a sweetheart or a token of affection are thus figurative extensions from the saint's feast day, which became a traditional occasion for expressing love.

The word is a proper name adopted into English. It is not productively formed from separable English morphemes.