Why is the ninth month called September?
1841, from French solidarité "communion of interests and responsibilities, mutual responsibility," a coinage of the "Encyclopédie" (1765), from solidaire "interdependent, complete, entire," from solide (see solid (adj.)). With a capital S-, the name of an independent trade union movement in Poland, formed September 1980, from Polish Solidarność.
A labor union in Poland, independent of the government and of the Polish Communist party, that grew to a membership of several million in the early 1980s. Led by Lech Walesa, Solidarity pushed for many reforms and played a major part in the ouster of communism in Poland and its replacement by a multiparty, democratic government. The movement's influence began to decline in the 1990s.