IPA: //ˌʌltrəˈmaɪkroʊtoʊm//
KK: /ˌʌltrəˈmaɪkroʊtoʊm/
A tool used to cut very thin slices of materials, especially for examining them under an electron microscope.
The scientist used an ultramicrotome to prepare samples for detailed analysis.
Ultramicrotome is formed from "ultra-" (meaning beyond) and "micro-" (meaning small) and "tome" (from Greek "tomos", meaning to cut). The word refers to a device that cuts specimens into extremely thin slices, going beyond the usual small size.
Think of 'beyond' ('ultra-') and 'small' ('micro-') to remember that an ultramicrotome is a tool that cuts things into very thin slices, even smaller than usual.
No commonly confused words.