As a noun, a sum is the total you get when you add numbers together, or a particular amount of money. As a verb, to sum means to add things up or to briefly state the main points.
From Latin 'summa' meaning 'total, highest, sum', from 'summus' (highest). It connected the idea of 'the top' with the 'final total'.
The 'sum' of something is like the peak of a mountain range of details—the final height after everything stacks up. That’s why 'to sum up' a talk means giving the highest‑level version of it.
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