(figuratively) The act of believing in something despite lack of proof of its truth or existence, or the attempt of something without being sure of its possible outcome.

(quantum mechanics) The discontinuous change of the state of an electron in an atom or molecule from one energy level to another. / (figuratively) An abrupt, extreme change.

A second of time added to the year occasionally to compensate for variation in the rate of Earth's rotation relative to the absolute standards of time.

An extra day intercalated into a year, especially the day intercalated into the Julian calendar every fourth year and into the Gregorian calendar every fourth year excepting centuries not divisible by 400, usually reckoned as February 29th.

A year in the Julian or Gregorian calendars with an intercalary day added to February, used to adjust for the extra hours of the solar year; a 366-day year.

plural of leap year

A nickname for a vehicle. / A nickname for someone or something that leaps. / The name given to a 1954 Cold War hero pigeon.

In the Jewish calendar or other lunisolar calendars, an extra month added to the usual 12 months because the solar year is slightly longer than 12 lunar months.

In the calendar reform, a week added to usual 52, such that every year starts on the same day

Third-person singular simple present indicative form of leap-frog