'austere' originates from Latin, specifically the word 'austerus', where 'austerus' meant 'harsh, severe'. The noun 'austereness' is formed in English by adding the suffix '-ness' to 'austere'.

'austere' passed into English via Old French 'austere' and Medieval Latin 'austerus'; the English noun-forming suffix '-ness' (from Old English '-nes(s)e') was later attached to create forms such as 'austereness'.

Initially, the root meant 'harsh' or 'severe'. Over time the sense broadened to include 'sternness' and also 'plainness' or 'lack of ornament', giving the modern senses of both strictness and simplicity.