Origin and history of Guido

late 14c., "to lead, direct, conduct," from Old French guider "to guide, lead, conduct" (14c.), earlier guier, from Frankish *witan "show the way" or a similar Germanic source, from Proto-Germanic *witanan "to look after, guard, ascribe to, reproach" (source also of German weisen "to show, point out," Old English witan "to reproach," wite "fine, penalty"), from PIE root *weid- "to see." The form of the French word influenced by Old Provençal guidar (n.) "guide, leader," or Italian guidare, both from the same source. Related: Guided; guiding. Guided missile, one capable of altering course in flight, is from 1945.

1721, in reference to the system of musical notation devised by Guido d'Arezzo, who lived early 11c.

"fellow," 1847, American English; earlier, in British English (1836) "grotesquely or poorly dressed person," originally (1806) "effigy of Guy Fawkes," a key figure in the Gunpowder Plot to blow up British king and Parliament (Nov. 5, 1605). He was the one caught with the gunpowder when the plot was revealed. The effigies were paraded through the streets by children on the anniversary of the conspiracy. The male proper name is from French, related to Italian Guido, which form Fawkes also sometimes used.