'mixed-origin' originates from English, specifically the compound of the adjective 'mixed' and the noun 'origin', where 'mixed' ultimately comes from Latin 'miscēre' (via Old French 'mixer'/'mixte') meaning 'to mix' and 'origin' comes from Latin 'origo' meaning 'beginning or source'.

'mixed' changed from Latin 'miscēre' into Old French forms such as 'mescler/mixte' and then into Middle English 'mix(e)d' (past participle), while 'origin' changed from Latin 'origo' into Old French 'origine' and then Middle English 'origin', and these elements were combined in modern English to form the compound 'mixed-origin'.

Initially the parts meant 'combined' (for 'mixed') and 'beginning/source' (for 'origin'); over time the compound came to denote something whose source or ancestry is composed of multiple distinct origins.