a transit instrument provided with a graduated vertical scale, used to measure the declinations of heavenly bodies and to determine the time of meridian transits.
Astrology. the passage of a planet in aspect to another planet or a specific point in a horoscope.
6.
Surveying.
a.
Also called transit instrument.an instrument, as a theodolite, having a telescope that can be transited, used for measuring horizontal and sometimes vertical angles.
b.
a repeating transit theodolite.
7.
(initial capital letter) U.S. Aerospace. one of a series of satellites for providing positional data to ships and aircraft.
–verb (used with object)
8.
to pass across or through.
9.
Surveying. to turn (the telescope of a transit) in a vertical plane in order to reverse direction; plunge.
10.
Astronomy. to cross (a meridian, celestial body, etc.).
–verb (used without object)
11.
to pass over or through something; make a transit.
12.
Astronomy. to make a transit across a meridian, celestial body, etc.
Origin: 1400–50; late ME (n. and v.) < L trānsitus a going across, passage, equiv. to trānsi-, var. s. of trānsīre to cross (trāns-trans-+ -īre to go) + -tus suffix of v. action
The passage of a smaller celestial body or its shadow across the disk of a larger celestial body. As observed from Earth, Mercury and Venus are the only planets of the solar system that make transits of the Sun, because they are the only planets with orbits that lie between Earth and the Sun. Mercury makes an average of 13 transits of the Sun each century. Transits of Venus across the Sun are much rarer, with only 7 of them having occurred between 1639 and 2004. In contrast, transits of Jupiter's moons across its disk are common occurrences. Compare occultation.
The passage of a celestial body across the celestial meridian (the great circle on the celestial sphere passing through the celestial poles and an observer's zenith). For any observer, the object is at its highest in the sky at its transit of the observer's meridian. See more at celestial meridian.
[tran-sit, -zit] 
noun, verb, -sit⋅ed, -sit⋅ing.