'co-chair' originates from the prefix 'co-' (from Latin 'com-', meaning 'together') combined with 'chair'. 'Chair' originates from Old French 'chaiere', ultimately from Latin 'cathedra' meaning 'seat'.

'co-' developed from Latin 'com-' into the English combining form 'co-'; 'chair' changed from Old French 'chaiere' (from Latin 'cathedra', from Greek 'kathédra') to Middle English forms such as 'chaire' and eventually became the modern English 'chair'. The compound 'co-chair' arose by combining the prefix with the modern noun/verb 'chair' to mean 'jointly preside'.

Initially 'chair' referred to a 'seat' (from Latin 'cathedra'), but over time it came to mean the person who presides over a meeting; combined with 'co-' ('together'), 'co-chair' evolved to mean 'to preside jointly' and 'co-chaired' means 'presided jointly' or 'having been presided jointly'.