'understandability' is built from the verb 'understand' plus the suffixes '-able' and '-ity'. 'Understand' originates from Old English 'understandan' (under- + standan), '-able' comes from Latin '-abilis' via Old French, and '-ity' comes from Latin '-itas' via Old French.

'understand' comes from Old English 'understandan', which became Middle English 'understanden' and then modern English 'understand'. The adjective 'understandable' was formed by adding the suffix '-able' to 'understand', and 'understandability' was later formed by adding '-ity' to 'understandable' in Modern English.

Initially, elements of 'understand' had senses related to 'stand among/among' (Old English components), but over time 'understand' came to mean 'grasp the meaning', and 'understandability' evolved to mean 'the quality of being graspable or clear'.