What does bissextile mean?
Bissextile describes anything pertaining to a leap year, most commonly the additional day inserted into the calendar to keep it synchronised with the Earth's orbit around the Sun. In the Julian and Gregorian calendars this is 29 February, and the adjective appears chiefly in scholarly, historical, or calendrical writing — phrases such as 'bissextile year' and 'bissextile day' are its typical habitats. As a noun, 'bissextile' can itself denote a leap year, though this use is now rare. The word derives from Latin bissextus, literally 'twice sixth', because in the old Roman system the leap day was created by counting the same day — the sixth before the Kalends of March — twice over. Today 'leap year' has almost entirely displaced it in ordinary usage, but 'bissextile' survives as an elegant, precise term for readers interested in how civilisations have wrestled time into order. Its connotations are technical rather than poetic: it signals expertise about calendars rather than everyday familiarity.
Relating to a leap year or to the extra day intercalated in one (29 February).
"The bissextile day falls at the end of February every fourth year, subject to Gregorian adjustments."
Almost always found in the fixed phrases 'bissextile year' and 'bissextile day'; rarely used freely.
A leap year.
"Every bissextile brings 24 February's double count back into liturgical calendars."
Now rare; 'leap year' is the standard term.
Only when used as the noun meaning 'leap years'; the adjective does not inflect for number.
"The old almanac listed all the bissextiles of the century."
The extra February day was once counted twice as 'the sixth day before the Kalends of March' — literally 'twice-sixth', which is where 'bissextile' comes from.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of bissextile
Bissextile comes from Latin bissextus, a compound of bis ('twice') and sextus ('sixth'), referring to the Roman practice of doubling the sixth day before the Kalends of March to create a leap day. Medieval Latin bissextilis carried the sense into English, where it is attested from around the early modern period. It shares its Latin roots with other sex-based numerical words such as 'sextile'.
Related word forms
How bissextile is actually used
A formal, learned term used mainly in historical, calendrical, and technical contexts; in everyday speech 'leap year' is preferred.
Easily confused with bissextile
'Sextile' is a statistical or astrological term denoting a 60-degree aspect or interval, while 'bissextile' refers specifically to leap years and their extra day.