'agrammatical' originates from Greek, specifically the word 'agrammatos,' where 'a-' meant 'not' and 'grammatos' meant 'lettered' or 'grammatical'.

'agrammatos' transformed into the Late Latin word 'agrammaticus,' and eventually became the modern English word 'agrammatical'.

Initially, it meant 'not lettered or not grammatical,' and this meaning has largely remained the same in modern usage.