nuance
Meaning: a slight variation in meaning, tone, expression
Usage: The nuances of the poem were not obvious to the casual reader, but the professor was able to point them out.
dialect
Meaning: a variation of a language
Usage: In the country’s remote, mountainous regions, the inhabitants spoke a dialect that the country’s other inhabitants had difficulty understanding.
colloquial
Meaning: characteristic of informal conversation
Usage: Adam’s essay used too many colloquial expressions for a formal assignment.