Is it ensure, insure, or assure?
c.1400, "body of attendants; also "meeting of armed forces" (mid-15c.); main modern sense of "coming together of people, a meeting" is from 1520s; from Latin congressus "a friendly meeting; a hostile encounter," past participle of congredi "meet with, fight with," from com- "together" (see com-) + gradi "to walk," from gradus "a step" (see grade (n.)).
Sense of "meeting of delegates" is first recorded 1670s. Meaning "sexual union" is from 1580s. Used in reference to the national legislative body of the American states since 1775 (though since 1765 in America as a name for proposed bodies). Congress of Vienna met Nov. 1, 1814, to June 8, 1815, and redrew the map of Europe with an eye to creating a balance of powers after the disruptions of Napoleon.
The legislative branch of the United States federal government, composed of the House of Representatives and the Senate. Popularly elected, senators and representatives are responsible for advocating the interests of the constituents they represent. Numerous congressional committees are organized to study issues of public policy, recommend action, and, ultimately, pass laws. Congress plays an important role in the system of checks and balances; in fact, the two-house (bicameral) organization of Congress acts as an internal check, for each house must separately vote to pass a bill for it to become a law. In addition to lawmaking, Congress has a variety of functions, including appropriation of funds for executive and judicial activities; instituting taxes and regulating commerce; declaring war and raising and supporting a military; setting up federal courts and conducting impeachment proceedings; and approving presidential appointments.