Lewis Short
(verb) : frātercŭlo, āre, fraterculus, a word comically formed by Plautus, after the analogy of sororiare, and also used of the breasts
* To swell up alike (v. sororio), Plaut. Fragm. ap. Fest. p. 297 Müll.; cf. also FRATRARE.
Charlton T. Lewis, Charles Short, A Latin Dictionary