VERB (2)

1. cause to bulge out or project;

2. form a rounded prominence;
- Example: "The starved child's belly protuberated"

The Collaborative International Dictionary of English v.0.48:

Protuberate \Pro*tu"ber*ate\, v. i. [L. protuberare; pro forward
   + tuber a hump, protuberance. See Tuber.]
   To swell, or be prominent, beyond the adjacent surface; to
   bulge out. --S. Sharp.
   [1913 Webster]