c.1290, "quantity or amount of money," from Anglo-Fr. and O.Fr.
summe (13c.), from L.
summa "total number, whole, essence, gist," noun use of fem. of
summus "highest," from PIE
*sup-mos-, from base
*uper "over" (see
super-). The sense development from "highest" to "total number" is probably via the Roman custom of adding up a stack of figures from the bottom and writing the sum at the top, rather than at the bottom as we do now (cf.
the bottom line). Meaning "total number of anything" is recorded from c.1374. Meaning "essence of a writing or speech" also is attested from c.1374. The verb is attested from c.1300; meaning "briefly state the substance of" (now usually with
up) is first recorded 1621.
Sum-total is attested from c.1395, from M.L.
summa totalis.
[suhm] 
,noun, verb, summed, sum⋅ming.