mantissa Mantispidae • mantistic · · · Info · Definitions · Synonyms · Characters · · mantissa · · Text Latin · · Script 8 · · Length Definitions · · · (noun) the positive fractional part of the representation of a logarithm; in the expression log 643 = 2.808 the mantissa is .808. Synonyms: fixed-point part. · · Noun Definition 1 Synonyms · · · fixed-point part · · Synonym 1 Characters · · a latin small letter a U+0061 i latin small letter i U+0069 m latin small letter m U+006D n latin small letter n U+006E s latin small letter s U+0073 t latin small letter t U+0074