'single-nucleus' is a modern English compound combining 'single' (Old English root meaning 'one') and 'nucleus' (from Latin 'nucleus' meaning 'kernel' or 'core').

'nucleus' came from Latin 'nucleus' (diminutive of 'nux' meaning 'nut'), entered scientific Latin/English with the sense 'kernel' or 'central part', and in modern scientific English formed compounds such as 'single-nucleus' to describe cells with one nucleus.

Initially 'nucleus' meant 'kernel' or 'core' in Latin; over time, in biology it came to mean the cell's central organelle, and 'single-nucleus' now specifically denotes having one such organelle.