From The Collaborative International Dictionary of English v.0.48:
Plop \Plop\ (pl[o^]p), v. i. [imp. & p. p. Plopped (pl[o^]pt);
p. pr. & vb. n. Plopping.] [Imitative.]
1. To fall, drop, or move in any way, with a sudden splash or
slap, as on the surface of water.
[Webster 1913 Suppl.]
The body plopped up, turning on its side. --Kipling.
[Webster 1913 Suppl.]
From The Collaborative International Dictionary of English v.0.48:
plop \plop\ v. t.
1. to drop (something) so that it makes a plopping sound;
especially, to drop with the sound of something falling
into water. [WordNet sense 1, 2]
[WordNet 1.5]
2. To set down quickly, so as to make a sound; -- used often
with the reflexive; as, He plopped himself into the sofa.
[WordNet sense 3]
Syn: plank, flump, plonk, plunk, plump down, plunk down,
plump.
[WordNet 1.5]
From The Collaborative International Dictionary of English v.0.48:
Plop \Plop\, n.
Act of plopping; the sound made in plopping.
[Webster 1913 Suppl.]