Gallivant \GAL-uh-vant\ , verb;
1. To wander about, seeking pleasure or diversion; gad
2. To go about with members of the opposite sex
According to Etymonline.com:
This word is probably a 'humorous perversion' of gallant and it is attested from 1809.
Gallant dates to the early 15th century but at that time it meant "showy, finely dressed." It came from Old French galant which meant "courteous," but in the 14th century it meant "amusing, entertaining; lively bold." Galant is the present participle of galer ("make merry") and probably came from Frankish *wala- ("good, well") which came from Proto-Germanic *wal- which derived from Proto-Indo-European *wel- ("to wish, will"). The sense of gallant as being "politely attentive to women" was adopted in the 17th century, mimicking the French adoption of a similar definition. The noun gallant meaning "man of fashion and pleasure" dates to the mid-15th century, although it entered the language in the late 14th century with a meaning of "dissolute man, rake."
*Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Sunday, December 12