Normally, when you place the "de" prefix on a word, it becomes the opposite. This does not appear to be the case with "fenestrated" and "defenestrated". Why do the two words, which appear so similar, have meanings that are so different?
Google defines "fenestrated" as:
Provided with a window or windows. "the fenestrated heights of nearby buildings"
Having perforations, apertures, or transparent areas. "the capillaries have a fenestrated epithelium"
Google defines "defenestrated as:
Throw (someone) out of a window. "she had made up her mind that the woman had been defenestrated, although the official verdict had been suicide"
Remove or dismiss (someone) from a position of power or authority. "the overwhelming view is that he should be defenestrated before the next election"