addedly comes from added + -ly, from add, from Latin addere ('to add'), from ad- ('to') + dare ('to give'), from the Proto-Indo-European root *deh₃- ('to give'). Morphologically, the word is transparent: -ly is attached to the older base named in the history, so the modern form packages an inherited or borrowed stem inside a later English derivative. In modern use, the adverb sense is "in addition; as something further", which keeps the etymology connected to the word's present dictionary value rather than treating it as a merely historical label. The wider word family includes related English forms such as add, added, addition, showing how the same base continues to support neighboring English vocabulary. The principal historical forms in the chain include Latin addere, Proto-Indo-European *deh₃-, which anchor the explanation in named linguistic material.