What are Continents?

Continent - mid 16th cent. (denoting a continuous tract of land): from Latin terra continens ‘continuous land.’

According to this definition there are four continents. America, Afroeurasia, Australia and Antarctica
(maybe throw Greenland in there for good measure). In usage, however, the word continent does not keep
true to its definition. In the English speaking world there are seven continents, North America, South
America, Europe, Asia, Africa, Oceania and Antarctica. In Russia Europe and Asia are usually considered
one continent; Eurasia. 

These divisions are strange, Europe is certainly connected to Asia, and so is Africa if you look closely at
Egypt. There does not seem to be anything separating North and South America either. And what is up
with the Islands? Does Greenland belong to America or Europe? And where does polynesia go? The
worst about the seven continent world view in my opinion is that it gives Europe Special status as a
continent, and disregards the middle east and India. The latter is even taunted with the title subcontinent!
What makes India subpar compared to Europe?