I became curious about this when I realized that German and Welsh have the same word for window: Fenster and ffenestr, respectively.

Old Norse (north Germanic) vindauga (wind-eye)

Old English (west Germanic) éagþyrel (eye hole)

Modern English (west Germanic) window

Norwegian (north Germanic) vindu

Danish (north Germanic) vindue

German (west Germanic) Fenster

Dutch (west Germanic) venster

Swedish (north Germanic) fönster

Latin fenestra

French fenêtre

Old Norse, Old English, Modern English, Modern Norwegian, and Danish all have some version of the native Germanic “wind-eye” word. Modern German has Fenster, which was borrowed from Latin (fenestra) some time before or during the Old High German period. Dutch and Swedish may have borrowed this word either from German, French, or directly from Latin. I don’t know much about the history of Swedish and Dutch, but it seems reasonable to assume that the word was first acquired by German speakers in Rhineland who were in direct contact (& conflict) with Romans, and later diffused northward into other Germanic groups. Note that the words Fenster, venster, and fönster are practically identical in pronunciation, and all three drop the middle vowel, forming the nst consonant cluster and reducing the word to 2 syllables.
Note also that English does have the words defenestration/defenestrate which are borrowed from Latin, but these are obscure learned terms, not used in every day speech like our Germanic window.

Here’s where it gets interesting:

Welsh ffenestr

Middle Irish fuindeog

Irish fuinneog

Middle Gaelic fuinneog

Gaelic uinneag

Manx uinnag

all the Celtic words for ‘window’ listed above are derived from Old Norse, except for the Welsh ffenestr. According to the dictionary, English got defenestrate directly from Latin. Welsh probably got ffenestr from English or Latin. But why did the Latinate word come into common usage?