'assimilability' originates from Latin, specifically the word 'assimilare', where the prefix 'ad-' (in assimilare historically assimilated to 'as-') meant 'to/toward' and the root 'similis' meant 'like' or 'similar'. The modern noun is formed by adding the suffix '-ability' (denoting capacity) to a stem related to 'assimilate'.

'assimilability' developed from Latin 'assimilare' → Old French/Medieval Latin forms (e.g. French 'assimiler') → Middle English 'assimilaten'/'assimilate' (verb). The nominal abstract form was later created in Modern English by adding the suffix '-ability' to the verb stem, yielding 'assimilability'.

Initially derived meanings centered on 'making like' or 'rendering similar'; over time the sense broadened to refer to the capacity or ease with which something can be absorbed, integrated, or understood—the modern meaning of 'ability to be assimilated'.