A chromatosome is essentially a nucleosome with one bound linker histone. See: nucleosome and chromatin.
Details
A chromatosome consists of a histone octamer, one molecule of linker histone, for example, Histone H1 and 166bp of DNA. The linker histone is a binding agent, acting like a finger holding down the DNA preventing its release.
References
Chromatosome Wikipedia(Text) CC BY-SA