'unaesthetic' originates from the Old English prefix 'un-' meaning 'not' combined with 'aesthetic', which ultimately comes from Greek 'aisthētikos', where 'aisthēsis' meant 'perception' or 'sensation'.

'aesthetic' entered English via Latin and French from Greek 'aisthētikos'; the modern English adjective 'unaesthetic' was formed by prefixing the negative 'un-' to 'aesthetic'.

Initially, the root 'aisthētikos' related to 'perception' or 'sensation'; over time 'aesthetic' shifted to mean 'relating to beauty or artistic taste', so 'unaesthetic' came to mean 'not pleasing in appearance or lacking aesthetic quality'.