From The Collaborative International Dictionary of English v.0.48 [gcide]:
grounder \grounder\ (ground"[~e]r), n. (Baseball)
A batted ball that hits the ground before it leaves the
infield, or the act of hitting a baseball along the ground;
also called ground ball; -- contrasted with fly or {fly
ball}.
Syn: .
[WordNet 1.5]
From WordNet (r) 3.0 (2006) [wn]:
grounder
n 1: (baseball) a hit that travels along the ground [syn:
grounder, ground ball, groundball, hopper]