The Collaborative International Dictionary
Osculum \Os"cu*lum\, n.; pl. Oscula. [L., a little mouth.] (Zo["o]l.) Same as Oscule.
Wiktionary
n. (context biology English) the main opening in a sponge from which water is expelled.
Wikipedia
The osculum is an excretory structure in the living sponge, a large opening to the outside through which the current of water exits after passing through the spongocoel. Wastes diffuse into the water and the water exits through the osculum at a velocity of nearly 8.4 cm/second, carrying away with it the sponge's wastes. The size of the osculum is regulated by the myocyte. Its size, in turn, determines the amount of water flowing through the sponge.
Usage examples of "osculum".
Quibus valefaciens cum moerore Commisit suis fratribus natos cum uxore: Matremque deosculatos filiali more, Vix eam alloquitur cordis prae dolore, Illis mota viscera, corda tremuerunt, Dum alter in alterius colla irruerunt, Expetentes oscula, quae vix receperunt Propter multitudines, quae eos compresserunt.
He had known that the Osculum Cruentus had a reputation for harbouring horrors, but things here were worse than he could have imagined.
The ship was in jumpspace, heading off on the first of a series of programmed spatial leaps guaranteed to throw the Osculum off his trail.
When he needs breath he pulls the statue to him, the little grotesquerie hunched and glowing in the night sea with faint biotic light, the toothed osculum a puncture-hole of dark, the open eye wide and mocking, tar-black, and he kisses it deeply and feels its flickering tongue-thing with the disgust that he can never banish.