All Greek to me completely unintelligible. Greek for unintelligible language or gibberish is recorded from the late 16th century, as in Shakespeare's Julius Caesar (1599) when Casca, having said that Cicero spoke Greek, adds, ‘for mine own part, it was Greek to me.’
at the Greek calends never; the Greek Calends will never come as the Greeks did not use calends in reckoning time. The term is recorded from the mid 17th century.
Greek cross a cross of which all four arms are of equal length.
Greek fire a combustible composition emitted by a flame-throwing weapon, and used to set light to enemy ships, which was first used by the Greeks besieged in Constantinople (673–8). It ignited on contact with water, and was probably based on naphtha and quicklime.
Greek gift a gift made to conceal an act of treachery; the allusion is to the Trojan Horse, and to the warning timeo Danaos et dona ferentes ‘I fear the Greeks even when they bring gifts.’
Greek key a pattern of interlocking right-angled spirals.
Greek Orthodox Church the Eastern Orthodox Church which uses the Byzantine rite in Greek, in particular the national Church of Greece.
when Greek meets Greek, then comes the tug of war when two people of a similar kind are opposed, there is a struggle for supremacy. The saying is recorded from the late 17th century, and is found originally in Nathaniel Lee's The Rival Queens (1677), ‘When Greeks joined Greeks, then was the tug of war.’
See also fear the Greeks bearing gifts.