largeness of dimensions or scope; abundance
Such was his amplitude of learning, and such his copiousness of communication, that it may be doubted whether a day now passes, in which I have not some advantage from his friendship — Dr Johnson
the extent of a vibration or oscillation measured from the average position to a maximum
the maximum departure of the value of an alternating current or wave, e.g. a radio wave, from the average value
the position of the horizon between the true east or west point and the foot of a vertical circle passing through any star or object
[Latin amplitudo, from amplus ample + -tudo -tude]