sorbi

One verb for what a sponge does. Sorbi is to take a liquid into yourself: the ground drinks the rain, the cloth takes up the spill, the sablo swallows the wave. The subject is usually the thing doing the soaking rather than the liquid, and the liquid takes the accusative: la tuko sorbis la akvon.

The doublet, honestly. Esperanto also has absorbi, and dictionaries list it, so the fence needs stating. In practice sorbi is the everyday word and covers the physical business completely, while absorbi survives in two narrow places: the technical register, where a material absorbs radiation or heat, and the figurative one, where a person is absorbed in their work (absorbita de la laboro). If you learn one of the pair, learn this one. It is shorter, it is older in the language, and nothing it says needs the other.

The derivations are the useful part. Sorbeti, with the -et- diminutive, is to sip, which is soaking up in small mouthfuls and is what you do to hot tea. Sorbigi is to make something soak, ensorbi is to soak in, and sorbilo is an absorbent pad or blotter. Note the fence against trinki, rank 486: you trinkas on purpose, through your mouth, and a towel never does.