Select the most appropriate one-word substitution for the given group of words. 

Informal, less grammatically rigid language 

Colloquial

The most appropriate one-word substitution for the given group of words "Informal, less grammatically rigid language" is "Colloquial".

Explanation of the options:

1. Slang: Slang refers to a type of informal language that is specific to certain groups or communities. It often consists of unconventional words, expressions, or phrases that are not considered standard or formal.

2. Verbose: Verbose refers to using an excessive number of words or being overly wordy in speech or writing. It does not specifically relate to informal or less grammatically rigid language.

3. Colloquial: Colloquial refers to the use of language that is conversational, informal, and commonly used in everyday speech. It often deviates from strict grammatical rules and may include regional or cultural variations.

4. Equivocal: Equivocal refers to language or expressions that are intentionally ambiguous or open to multiple interpretations. It does not specifically capture the concept of informal or less grammatically rigid language.