Origins
The history of 'dinner' is both a linguistic story and a social history of when Europeans ate their main meal. Today, 'dinner' in British and American English typically refers to the evening meal, but this was not always the case — and the etymology preserves the older reality.
The word entered English in the 13th century from Old French disner or dîner, a verb meaning 'to eat the first main meal of the day'. This Old French verb descended from Vulgar Latin *disiēiūnāre, a compound formed from the prefix dis- (expressing reversal or removal) and iēiūnium (a fast, abstinence from food). To dis-iēiūnāre was to break a fast — to eat after a period of not eating. This is exactly the same etymological concept as English 'breakfast' (break + fast), but the two words arrived in English by completely different routes: 'dinner' came through Latin and French, 'breakfast' was coined directly in English from Germanic roots.
Latin iēiūnium is itself an interesting word. It derived from the adjective iēiūnus, meaning 'fasting' or 'hungry', and gave English the medical/anatomical term 'jejunum' — the middle section of the small intestine, so named because it was typically found empty in dissection. The adjective iēiūnus may also be the source of 'jejune' meaning 'naïve or simplistic', though this derivation is debated.
Development
In medieval English, 'dinner' referred to the midday meal — the main meal of the day, typically taken between 10 AM and noon for working people, or around midday for the gentry. Supper was a lighter meal taken in the evening. This was the standard pattern through the medieval period and into the early modern era.
The shift of 'dinner' from midday to evening was a social and class phenomenon that unfolded over the 17th, 18th, and 19th centuries. As upper-class and then middle-class families adopted the fashion of dining later and later in the day — a sign of leisure, since it meant the main meal was not constrained by working hours — 'dinner' migrated with them. By the Victorian period, fashionable dinner was taken at 7 or 8 PM, and the midday meal had become 'lunch'. Working-class communities, whose main meal remained at midday, continued calling it 'dinner' — a distinction that persists in British English regional variation to this day, where some speakers say 'dinner' for the midday meal and 'tea' for the evening one.
The Old French verb disner (to dine) also gave English the verb 'dine' and the noun 'diner'. 'Diner' in the sense of a person who dines is 14th-century; 'diner' in the sense of an American roadside eating establishment dates to the 1930s, named for the railway dining car it resembled.
Latin Roots
French dîner and déjeuner both originally meant 'to break a fast', but through the same social drift that affected English, dîner shifted to the evening meal while déjeuner settled on the midday meal. The French petit déjeuner (breakfast, literally 'small lunch/fast-break') reflects this realignment. Across Romance languages — French, Spanish, Italian, Portuguese — the words for meals have undergone parallel but not identical shifts, with 'dinner' words migrating toward evening in most urban, middle-class speech communities.
The phrase 'dinner party' dates to the 18th century, and 'TV dinner' to 1954, when Swanson launched its frozen pre-portioned meal designed to be eaten in front of the television. This last compound neatly encapsulates the full journey: from a Latin word for sacred abstinence, through a medieval feast, to a tray of frozen food before the screen.