(van′gärd) noun
1. The advance guard of an army; the van.
2. Hence, one who or that which is foremost. [<OF avangarde, var. of avantgarde <avant before + garde guard]

noun
The second U. S. artificial satel-lite, launched from Cape Canaveral, Fla., on March 17, 1958, to a maximum altitude of 2,513 miles: diameter, 6.4 inches; weight, 3.25 pounds; equipment, two radio transmitters.