ETYM For vantguard, avantguard, French avant-garde; avant before, fore + garde guard. Related to Avant, Ab-,Ante-, and Guard, Advance, Vamp, Van of an army, Vaward.
1. The leading units moving at the head of an army; SYN. van.
2. The position of greatest advancement; the leading position in any movement or field; SYN. forefront, cutting edge.
Early series of US Earth-orbiting satellites and their associated rocket launcher. Vanguard 1 was the second US satellite, launched 17 March 1958 by the three-stage Vanguard rocket. Tracking of its orbit revealed that Earth is slightly pear-shaped. The series ended Sept 1959 with Vanguard 3.