Added as a supplement or attachment to something else, typically at the end.
From Latin appendere, combining ad- (to) + pendere (to hang). The word entered English in the 17th century, originally meaning to hang something from something else, evolving to mean adding supplementary material.
The image of 'hanging something on' perfectly captures how appendices and addenda work - they dangle from the main text like ornaments on a tree. This physical metaphor helps explain why we talk about 'hanging' additional clauses in sentences or 'tacking on' extra information.
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