I'm having trouble finding a definition of **telescope** that works for all telescopes (optical, radio, or otherwise). So far, all the definitions I've found only apply to **optical telescopes**. 

[ODO](https://en.oxforddictionaries.com/definition/telescope):

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> **telescope**  
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>  An optical instrument designed to make distant objects appear nearer, containing an arrangement of lenses, or of curved mirrors and lenses, by which rays of light are collected and focused and the resulting image magnified.
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[Dictionary.com](http://www.dictionary.com/browse/telescope): 

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> **telescope**  
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>  an optical instrument for making distant objects appear larger and therefore nearer. One of the two principal forms (refracting telescope) consists essentially of an objective lens set into one end of a tube and an adjustable eyepiece or combination of lenses set into the other end of a tube that slides into the first and through which the enlarged object is viewed directly; the other form (reflecting telescope) has a concave mirror that gathers light from the object and focuses it into an adjustable eyepiece or combination of lenses through which the reflection of the object is enlarged and viewed.
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These definitions work just fine for optical telescopes, but there are many different types of telescopes, and not all of them fit either definition. According to [Wikipedia](https://en.wikipedia.org/wiki/Telescope#Types), 

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> [In certain] types of high energy particle telescopes there is no image-forming optical system. 
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A telescope's optical components seem to be a defining feature, and I'm uncertain how some of these types of telescopes are considered telescopes under the current definition. 

Is there another, more generic definition of "telescope" that I've missed?
 If not, is there a reason why the definition of "telescope" hasn't been updated to include a wider range of devices?