If you're thinking about the rules of language:
* Ungrammaticality: This directly refers to a violation of grammatical rules.
* Incoherence: This implies a lack of logical or grammatical structure, making it difficult to understand.
* Chaos: This suggests a complete absence of order or structure, including grammatical rules.
* Illogicality: This focuses on the absence of logical coherence, which can sometimes be connected to grammar.
If you're thinking about the study of language:
* Ignorance: This refers to a lack of knowledge about grammar.
* Unfamiliarity: This means being unacquainted with the rules of grammar.
If you're thinking about the use of language in a specific context:
* Informal: This contrasts with formal grammar, implying a relaxed approach to language rules.
* Slang: This refers to casual and informal language that often deviates from standard grammar.
* Jargon: This refers to specialized language used by a particular group, which may have its own grammatical rules.
Ultimately, the best antonym for "grammar" depends on the specific context and what you're trying to express.