'mononasal' originates from Greek and Latin elements: Greek 'mono-' (from 'mónos') meaning 'single, one' and Latin 'nasalis' (from 'nasus') relating to 'nose'.

'mononasal' was formed in Modern English by combining the prefix 'mono-' with the adjective 'nasal' (itself from Latin 'nasalis'); it reflects a direct compound rather than a long historical phonological change.

Initially it literally combined 'one' + 'nose' to denote a single nasal opening; this specific anatomical/technical sense has remained the primary meaning in modern usage.