Relative Course. Course steered by another ship when expressed as the angle that course makes with course of one's own ship.
Relative Humidity. Humidity of atmosphere when expressed as a percentage of the humidity of saturated air.
Relative Magnitude of Star or Planet. Classification of its brightness compared with other stars as viewed from Earth, thus differing from 'absolute' magnitude. Is expressed as a number, which increases as brightness decreases. Stars of 6th magnitude and below can be seen with naked eye. Luminosity of any star is 2.512 times that of a star one above it in relative magnitude.
Release. To set free. In engineering, is applied to the moment when steam is first allowed to escape from cylinder. In ship's business, means a discharge from a contracted undertaking. To release a ship is to withdraw all opposition to her sailing or movement. To release cargo is to authorise its removal from ship.