Something added or an addition; an alternative archaic or rare term for something added to something else.
From Latin addimentum (an addition), from addere (to add). The suffix '-ment' creates nouns from verbs in Latin-derived English words.
Most people use 'addendum' today, but 'addiment' is its forgotten cousin—both come from the same Latin root, showing how English kept extra synonyms from the Middle Ages that mostly vanished.
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