Origin and history of Bundestag

mid-14c., ajournen, "assign a day, fix a day" (for convening or reconvening of an organized body), from Old French ajorner (12c.) "meet" (at an appointed time), from the phrase à jorn "to another day, to a (stated) day," from à "to" (see ad-) + journ "day," from Latin diurnus "daily," from dies "day" (from PIE root *dyeu- "to shine").

The notion is of setting a date for re-meeting. The meaning "close a meeting" (with or without intention to reconvene) is from early 15c. The sense of "go in a body to another place" (1640s) is colloquial.

The English word has had the -d- since 16c., but the spelling is unetymological, as the compound apparently is not from Latin; Middle French also occasionally has adjourner, but this was rejected in Modern French. Related: Adjourned; adjourning.

"an organized group," originally especially of armed men, late 15c., from French bande, which is traceable to the Proto-Germanic root of band (n.1), perhaps via a band of cloth worn as a mark of identification by a group of soldiers or others (compare Gothic bandwa "a sign"). But perhaps it is rather from Middle English band, bond in the sense "force that unites, bond, tie" (late 14c.). Also compare Old Norse band "cord that binds; act of binding," also "confederacy."

The extension to "group of musicians" is c. 1660, originally musicians attached to a regiment of the army and playing instruments which may be used while marching. To beat the band (1897) is to make enough noise to drown it out, hence to exceed everything. One-man band is recorded by 1931 in the sense of "man who plays several musical instruments simultaneously;" the figurative extension is attested by 1938.