English
pseudospectrum
From pseudo- + spectrum.
Formed from pseudo- + spectrum
Proto-Indo-European *speḱ- ‘to see, to look, to observe’
Proto-Indo-European *spéḱyeti ‘to be looking at, to keep looking at’
Proto-Italic *spekjō ‘to observe, see’
Latin speciō ‘look at, view’
Latin spectrum ‘appearance, image, apparition’
English spectrum
Today it means
noun A set containing the spectrum of an operator and the numbers that are "almost" eigenvalues.
Language periods are conventional ranges, not dates for this word.
Etymograph / pseudospectrum