Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
sponge (n., v.)
To sponge on (off) someone is “to be a parasite, to use another’s resources without paying for them”; it’s Conversational and pejorative. To be a sponge is “to soak up drink or information or whatever there is to be absorbed.” The noun is frequently not pejorative in its figurative senses: A bright youngster enthralled with a new subject can be a sponge and be admired for it. An idiom with the literal sense of the noun comes from prizefighting: to throw in (or throw up) the sponge—when a second throws into the center of the ring the sponge he’s been using on his fighter between rounds, he’s signaling that his fighter is beaten: “We quit.” To throw in the towel is a variant with the same meaning. We use both today in all sorts of activities: they’re colorful clichés, Conversational and Informal.
