'mononucleated' originates from Greek and Latin elements: Greek 'mono-' (from 'monos') meaning 'single' and Latin 'nucleus' meaning 'kernel' or 'core', combined in modern scientific English to form the adjectival/participle form.

'mononucleated' developed from the adjective/verb 'mononucleate' (formed in modern scientific/Modern Latin usage), which itself combines Greek 'mono-' + Latin 'nucleus'; the English adjective/past-participle 'mononucleated' arose as the regular participial/adjectival form.

Initially it literally referred to having a single 'kernel' or 'core' (nucleus); over time it came to be used specifically in biology to mean 'having one cell nucleus.'