'assimilation' originates from Latin, specifically the word 'assimilatio', where the prefix 'ad-' (assimilated as 'as-') meant 'to/toward' and 'similis' meant 'like'.

'assimilation' changed from Latin 'assimilatio' into Old French/Medieval Latin forms and then entered Middle English as 'assimilation' (or similar spellings), eventually becoming the modern English word 'assimilation'.

Initially, it meant 'the act of making similar' or 'making like'; over time the term broadened to include cultural, linguistic, and biological senses but retained the core idea of 'becoming similar' or 'being made similar'.