Amplitude

Am·pli·tude

State of being ample; extent of surface or space; largeness of dimensions; size.
The cathedral of Lincoln . . . is a magnificent structure, proportionable to the amplitude of the diocese.
— Fuller.
Largeness, in a figurative sense; breadth; abundance; fullness.
The arc of the horizon between the true east or west point and the center of the sun, or a star, at its rising or setting. At the rising, the amplitude is eastern or ortive: at the setting, it is western, occiduous, or occasive. It is also northern or southern, when north or south of the equator. (Astron.)
The horizontal line which measures the distance to which a projectile is thrown; the range. (Gun.)
The extent of a movement measured from the starting point or position of equilibrium; -- applied especially to vibratory movements. (Physics)
An angle upon which the value of some function depends; -- a term used more especially in connection with elliptic functions. (math.)

Magnetic amplitude: the angular distance of a heavenly body, when on the horizon, from the magnetic east or west point as indicated by the compass. The difference between the magnetic and the true or astronomical amplitude (see 3 above) is the “variation of the compass.”