negative definite
Mathematics
adjective
1(Of a function) having negative (formerly: negative or zero) values for all non-zero values of its argument.
2(Of a square matrix) having all its eigenvalues negative.
3(Of an operator on a Hilbert space) such that the inner product of any element of the space with its image under the operator is less than zero.
Origin
Mid 19th century; earliest use found in Proceedings of the Royal Society of London.