'ungrammatical' originates from the prefix 'un-' meaning 'not' and the word 'grammatical', which comes from the Greek word 'grammatikos', meaning 'pertaining to letters or learning'.

'Grammatical' transformed from the Greek word 'grammatikos' through Latin 'grammaticalis', and eventually became the modern English word 'grammatical'. The prefix 'un-' was added to form 'ungrammatical'.

Initially, 'grammatikos' meant 'pertaining to letters', but over time it evolved to mean 'conforming to grammar rules', and 'ungrammatical' as its opposite.