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X-ray
/ˈɛks-reɪ/ (say 'eks-ray),
/ɛks-ˈreɪ/ (say eks-'ray)

noun 1. (often plural) Physics electromagnetic radiation of shorter wavelength than light (5 × 10-9 to 6 × 10-12 m) which is able to penetrate solids, ionise gases, and expose photographic plates; roentgen ray.

2.  an examination of the interior of the body of a person or animal or the interior of an opaque substance by means of an apparatus using X-rays.

3. → radiograph (def. 1).

–verb (t) 4.  to examine by means of X-rays.

5.  to make an X-ray radiograph of.

6.  to treat with X-rays.

[German: translation of X-strahlen, so called because their nature was not known; coined in 1895 by their discoverer WK Roentgen, 1845–1923]