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semi-sum
semi-sum n. 
/ˈsɛmiˌsəm/ half the sum of two or more quantities.
Brit. /ˈsɛmɪsʌm/
, /ˈsɛmɪsʌm/U.S. /ˈsɛˌmaɪˌsəm/
, /ˈsɛˌmaɪˌsəm//ˈsɛmiˌsəm/ΘΚΠ
the world > relative properties > number > arithmetic or algebraic operations > [noun] > summing or addition > result of > half of
semi-sum1766
1766 W. Ludlam in Philos. Trans. 1765 (Royal Soc.) 55 210 ACK is the semi-sum, and DAI the semi-difference of the angles CAI, CIA.
1873 Rep. Brit. Assoc. i. 23 The semi~sum and semidifference of the numbers to be multiplied.
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