leap years

Noun

leap year (plural leap years)

1. A year in the Julian or Gregorian calendar with an intercalary day added to February (in the Gregorian calendar, February 29), used to adjust for the extra hours of the solar year; a 366-day year.
   • The additional day which occurred every fourth year [after the Julian Reform] was given to February, as being the shortest month, and was inserted in the calendar between the twenty-fourth and twenty-fifth day. February having then twenty-nine days, the twenty-fifth was the sixth of the calends of...1842, “CALENDAR”, in The Encyclopædia Britannica or Dictionary of Arts, Sciences, and General Literature. […], 7th edition, volume VI, Edinburgh: Adam and Charles Black, →OCLC, page 5, column 2

   Synonyms:

   bissext, bissextile, bissextile year, intercalary year

2. (broadly) Any other year featuring intercalation, such as a year in a lunisolar calendar with 13 months instead of 12, used to maintain its alignment with the seasons of the solar year.