Enosis is the Greek word for "union". In Modern Greek history, it has primarily been used to signify the unification to the independent Greek state, of an unredeemed part of the Greek nation (e.g. Crete and much more recently Cyprus).
In 1830, after the Greek Revolution, Greece was recognised as an independent state. The newly-independent state, however, comprised little more than Peloponnesus, Rumeli and the Cyclades island complex. Fully two-thirds of the Greek nation was left outside its borders. This included Greeks in Thessaly, Epirus, Macedonia, Thrace, western Asia Minor, Pontus, several Aegean islands including Crete, Chios, Lesbos and Samos plus the island of Cyprus.
Some, like Samos, had limited autonomy but the majority had little say in their future and yearned to unite with their brethren in the Greek State. For them the word "Enosis" became a rallying cry.
After the First Balkan War, most of the islands of the Aegean Sea were united with Greece as was the independent state of Crete. After the Asia Minor disaster, more than 1,000,000 Greeks of Asia Minor came to Greece as refugees. After World War II, the Dodecanese were re-united with their Greek brethren so, in the post-WW II years, "Enosis" has been used nearly exclusively to mean the union of Cyprus, a British colony until 1960 and "independent" state since, with the Greek state.
Enosis was sought by the Greek majority of Cyprus since the British arrived on the island. In greeting the first British governor, the Archbishop of Cyprus made him aware of his flock's wishes concerning the future of the island.
In 1931, frustration over British apathy towards their aspirations led Cypriots to demonstrate in Lefkosia and throughout Cyprus. The heavy-handed British response turned the demonstrations into riots with several government buildings burned down.
Finally, on April 1, 1955, after all previous actions had failed, the Cypriots resorted to armed struggle forming the military organisation EOKA whose one and only aim was Enosis with Greece. The British refused to give in and, in 1960, following the treaties of London and Zurich, the Republic of Cyprus was proclaimed. As Samos and Crete had also gone through a period of independence prior to their unification with the mother country, many Cypriots also hoped that would be the case with them. To date, Enosis in their case has not been achieved.