Cebar
To serve the mate — fill the gourd, pour the water, hand it over and run the circle. The most socially loaded verb in Uruguay.
Related lesson: Uruguayan Spanish: A Survival Guide.
Hear it in context
—¿Quién ceba? —Yo, que traje el termo.
'Who's serving?' 'Me — I brought the thermos.'
Cebame uno más y arrancamos.
Pour me one more and we'll get going.
Lo cebó mal y quedó lavado a los tres mates.
She poured it badly and it was washed out after three rounds.
What It Actually Means
Cebar is to prepare and serve mate: to arrange the yerba on its slope inside the gourd, wet it, place the bombilla, pour the hot water from the thermos, and hand the gourd to the next drinker. The person doing it is the cebador or cebadora, and the role is a real one — they control the order, the temperature and the pace, and the gourd returns to them after every single drinker. It is used absolutely (yo cebo), transitively on the drink (cebar un mate) and with an indirect object for the person (cebame uno).
Where It Comes From
From cebar, to feed or fatten an animal, and by extension to prime something — a pump, a fire, a firearm. Feeding the gourd its water is the same metaphor, and the verb has meant this in the Río de la Plata for as long as anyone has written the practice down. Nothing exotic and nothing invented: it is the ordinary Spanish verb doing an extraordinary amount of cultural work.
How Natives Use It
As plain vocabulary, not slang, and shared with Argentina, Paraguay and southern Brazil — Uruguay’s claim is one of volume rather than ownership. What is distinctly Uruguayan is the portability: the thermos under the left arm, the gourd in the right hand, on the bus, in a queue, walking the rambla. Uruguayan mate is bitter, finely ground, very hot, and refilled without ceremony, so somebody is cebando more or less continuously.
Common Pitfall
The etiquette is the pitfall, and it is unforgiving. Do not touch the bombilla — not to stir, not to straighten it. Do not pass the gourd on to the next person; it goes back to the cebador. Drink it dry, noise and all. And say gracias only when you have finished for good, because in this one context it means “I’m out”, not “how kind” — thank the cebador on the first mate and you have politely resigned from the circle. One more trap: in Argentina the reflexive cebarse has a separate slang life meaning to get carried away or over-excited, which has nothing to do with the drink.