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Etymologists generally agree that the English word was derived from the French "hangar" in the mid-19th century.
The OED (Oxford English Dictionary) claims that the etymology beyond that is uncertain. One possible source of the French form is Medieval Latin angarium "a shed in which horses are shod".
Then there's a Middle French version of the word, hanghart, which may very well be an alteration of Middle Dutch *ham-gaerd or *haim-gard, both being the equivalents of English hamlet + garden and referring to a group of buildings enclosed by a fence (gard is cognate with English yard and garden). However, the asterisks before the Middle Dutch words indicate that they are theoretical words and are not documented in written form. Nevertheless, they are logical formations and could very well be the ultimate source of hangar.
The English form of the word first applied to sheds which were used to house coaches, and it is easy to see how that sense could have developed from either ungarium or *ham-gaerd, and further how it could have later taken on the sense "shed or building for storing aircraft". There is a possibility that "hanging" had some impact on the use of this word in aviation, but the idea that it is somehow related to someone named Hangar has little support.