Mathematics. the decimal part of a common logarithm. Compare characteristic(def. 3a).
2.
Obsolete. an addition of little or no importance, as to a literary work.
Origin: 1860–65; < L, var. of mantisa addition, makeweight, said to be from Etruscan; logarithmic mantissa so called because it is additional to the characteristic or integral part (term introduced by H. Briggs)
decimal part of a logarithm, 1641, from L. mantisa "a worthless addition, makeweight," probably from a Gaulish word introduced into L. via Etruscan (cf. O.Ir. meit, Welsh maint "size").
mantissa 1. The part of a floating point number which, when multiplied by its radix raised to the power of its exponent, gives its value. The mantissa may include the number's sign or this may be considered to be a separate part. 2. The fractional part of a logarithm. (1996-06-15)