1the action or process of lengthening something:the bird’s tails become forked through elongation of their outer feathers [count noun]:an elongation of the crater in the impact direction
an elongated part.
the amount of extension of an object under stress, usually expressed as a percentage of the original length.
2 Astronomy the angular separation of a planet from the sun or of a satellite from a planet, as seen by an observer:Mercury reaches greatest elongation on the 1st, when it will be 27 degrees west of the Sun
late Middle English: from late Latin elongatio(n-), from elongare 'place at a distance' (see elongate)