40

The English word "quarantine" derives from the Venetian "quaranta giorni" (forty days) — the isolation period imposed on ships arriving from plague-affected ports in 14th–15th century Venice.

Forty days and forty nights appears in the Genesis flood narrative and recurs across the Hebrew Bible and New Testament for periods of testing or preparation. The repetition is a literary convention of the texts rather than a measured duration.

In the Hebrew Bible and the New Testament, forty recurs as the length of a period of trial or preparation — the flood, the wilderness years, the fast in the desert. Read by most scholars as a conventional round number for a long but bounded period rather than as an exact count, which is why it recurs across otherwise unrelated narratives. English 'quarantine' descends from the Venetian quaranta giorni by the same logic. This is a scholarly account rather than the tradition's own framing.

40 days and nights of rain is the duration given for the flood in the Genesis narrative (Hebrew Bible/Old Testament); 40 years of wilderness wandering appears in the Exodus narrative, and 40 days of fasting/temptation in the wilderness appears in the Christian Gospels' account of Jesus.

Forty recurs across Hebrew and later Christian and Islamic texts as a duration. Scholarship generally reads it as idiomatic — a long but finite period — rather than as a count, which explains its frequency better than coincidence does.

In Christianity, Lent runs for forty days before Easter, counted without the Sundays, in reference to the forty days described in the wilderness.

Presented as belief or tradition, not as an established fact.

There are 40 channels in the Citizens Band allocation (the United States and much of Europe; other countries differ). The United States allowed 23 until 1977. Channel 19 became the informal road channel and channel 9 the emergency one, neither by regulation in the first instance.

The distance to Proxima Centauri is about 40 trillion kilometres (the Milky Way). 4.2 light-years. Written in kilometres the number stops meaning anything, which is the argument for the light-year as a unit.

Quarantine derives from the Venetian quaranta giorni, the forty days ships were held before landing during plague outbreaks. The practice moved to other intervals long ago while the word kept the original number.

A 40-year anniversary is named for ruby. Stable across lists, and used institutionally as well as for marriages.

Forty is treated as a landmark birthday across much of the anglophone world, carrying both the 'life begins at 40' idiom — from Walter Pitkin's 1932 book of that title — and the 'over the hill' one. It has no legal or biological content whatever; it is a round number in a decimal culture.

Tennis scores 15, 30, 40 rather than 1, 2, 3. The most common explanation is a clock face marking quarters, with 45 shortened in speech to 40; the evidence is circumstantial, and the scoring predates any single documented account of why.