/əˈfɛər/
[noun] A matter, event, or situation that someone is involved in or concerned with; also used to describe a romantic or sexual relationship between two people, especially one that is secret.
'Affair' literally meant 'to do what you have to do' — it was never meant to be scandalous.
The word 'affair' arrived in English during the 13th century, carried across the Channel by the French-speaking Norman ruling class who had dominated England since 1066. It came directly from the Old French phrase 'a faire', which meant simply 'to do' — as ordinary and practical as a shopping list. The Old French 'faire' descended from the Latin 'facere', meaning 'to do' or 'to make', one of the most productive and hardworking roots in all of Western language.
The Latin 'facere' is remarkably generous in its descendants. Through various paths of transmission, it gave English the words 'fact' (from Latin 'factum', 'a thing done'), 'factory' (Latin 'factoria', a place where things are made), 'fashion' (Old French 'façon' → Middle English 'facioun', meaning the way something is made), and even 'feat' (Old French 'fait' → Middle English 'fet', a deed or act). 'Affair' belongs to this same proud family — it is, at its heart, simply a thing that gets done.
When the word first settled into English, it was entirely respectable and businesslike. An 'affair' in the 14th and 15th centuries referred to a task, a piece of business, or a matter requiring attention — the kind of word you might find in a merchant's ledger or a royal decree. The plural, 'affairs', took on the sense of a person's overall business dealings and concerns, which is still visible today in phrases like 'foreign affairs' or 'a minister of state affairs'. It was the language of commerce, politics, and governance.
The romantic and scandalous meaning of 'affair' developed much later and far more gradually. By the 18th century, 'affair' had begun to be used as a polite, slightly indirect way of referring to a love relationship — the kind of euphemism that allowed people to speak about delicate matters in refined company without stating things too plainly. By the 19th century, and especially into the 20th, 'an affair' had settled firmly into its modern sense: a secret or illicit romantic relationship, often between a married person and someone who is not their spouse. The word had drifted a long way from its origins as a to-do list.
What makes 'affair' particularly interesting is how it kept both its dull, administrative meaning and its charged, romantic one at the same time. Today the word can describe an international diplomatic crisis ('a delicate affair between two nations'), a grand social event ('a black-tie affair'), a trivial incident ('a minor affair'), or a passionate secret love story — sometimes all in the same newspaper. Few words carry such a wide range of human drama within a single syllable of French practicality.