boing

Short definition from Wiktionary

Interjection

1. 1
   A representation of the sound of something bouncing.
2. 2
   A representation of the sound of something bouncing: Announcing the presence of large, pert breasts, which are bouncy.
3. 3
   A representation of the sound of something bouncing: Announcing the advent of male arousal (erection), via the metaphor of a spring springing energetically.

Noun

1. 1
   The sound made by an elastic object (such as a spring) when bouncing; the sound of a bounce.
2. 2
   Large breasts.

Verb

1. 1
   To make a boing sound or bouncing motion.