This separate dialect developed because of Newfoundland's history as well as its geography. Newfoundland, which was settled in the early 1600s, was one of the first areas settled by English speakers in North America. This has given the dialect time to develop. Newfoundland English was recognized as a separate dialect by the late 1700s when George Cartwright published a glossary of Newfoundland words. Newfoundland remained separate from Canada as a British colony until 1949. So, in comparison to the other provinces and territories, Newfoundland is a newcomer to the country. Geographically, Newfoundland is very isolated from the rest of Canada. It is an island in the Atlantic Ocean separated from the mainland by the Strait of Belle Isle which is frozen over from November to June and by a large region of sparsely populated sub-polar land.
Newfoundland English differs from Canadian English in vowel pronunciation (for example: in Newfoundland the words "fear" and "fair" are homonyms); in morphology and syntax (for example: in Newfoundland the word "bees" is used in place of the normally conjugated forms of "to be" to describe continual actions or states of being: "she bees short" instead of "she is short", but normal conjugation of "to be" is used in all other cases); in preservation of archaic adverbal-intensifiers (for example: in Newfoundland "that play was right boring" and "that play was some boring" both mean "that play was very boring").
The greatest distinction between Newfoundland English and Canadian English is its vocabulary. It includes many Eskimo and Native American words (for example: "tabanask" - a kind of sled), preserved archaic English words no longer found in other English dialects (for example: "pook" - a mound of hay), compound words created from English words to describe things unique to Newfoundland (for example: "stun breeze" - a wind of at least 20 knots), English words which have undergone a semantic shift (for example: "rind" - the bark of a tree), and unique words whose origins are unknown (for example: "diddies" - a nightmare).
Link to extensive Newfoundland English on-line dictionary http://www.heritage.nf.ca/dictionary/
Some examples taken from A Biography of the english Language by C.M. Millward