Vernacular is the native language or native dialect in a specific population. Different to a language of wider communication that is a second language or foreign language to the population, such as a national language or standard language. - It is a type of dialect. Dialect is "A regional or social variety of a language distinguished by pronunciation, grammar, or vocabulary, especially a variety of speech differing from the standard literary language or speech pattern of the culture in which it exists: Cockney is a dialect of English." - dialects of Ancient Greek. -The language peculiar to the members of a group, especially in an occupation; jargon: the dialect of science. (yahoo education dictionary) -The manner or style of expressing oneself in language or the arts. -A language considered as part of a larger family of languages or a linguistic branch. Not in scientific use: Spanish and French are Romance dialects. (yahoo education dictionary)

venacular = using plain, everyday, ordinary language / the plain variety of language in everyday use by ordinary people / the common name of an animal or plant as distinguished from its Latin scientific name, e.g., Today I ate some corn (corn = vernacular), but the scientific name of corn is "Zea Mays or Maize". dialect = a form of a language spoken in a particular geographical area or by members of a particular social class or occupational group, distinguished by its vocabulary, grammar, and pronunciation, e.g. The people in Shanghai speak Chinese differently. They speak (pronounce)Shanghainese, but the words are written the same way. You would also hear many different dialects as you travel throughout China, e.g., the dialects in Yunnan. So, Fdmaxey is right, they are similar, but I have always thought of vernacular as vocabulary, and dialect as the way people pronounce the words.

Vernacular and dialect are very close, with just a slight difference. They both refer to the common language spoken by people in an area, a group or a profession. Dialect tends to also include the accent with which people speak, in addition to the vocabulary and grammar. Vernacular is sometimes used that way, but more often it just refers to differences in language and grammar. At least, that is how I'd interpret it, from how I've seen the two words used.