The word is a modern English formation built upon the adjective 'grammatical,' which itself descends from the Latin grammaticus and ultimately the Greek grammatikós, meaning "of or for letters or literature." The Greek root stems from grámma (letter, written mark), tracing back to the Proto-Indo-European root gerbʰ- meaning "to scratch, carve." The Germanic negative prefix un-, with ancient Proto-Indo-European cognates, was attached to create a direct negation. Thus, the term's literal construction, "not grammatical," transparently conveys its meaning of violating the systematic rules governing language structure.

Structure: un (not) + grammatical (conforming to grammar) - un: A prefix of Germanic origin (Old English un-), meaning "not." It functions as a negative particle. - grammatical: An adjective of Latin and Greek origin, from grammatica (grammar). It functions as the base word describing conformity to grammar rules.