Meaning

noun a porous mass of interlacing fibers that forms the internal skeleton of various marine animals and usable to absorb water or any porous rubber or cellulose product similarly used

noun someone able to acquire new knowledge and skills rapidly and easily

noun a follower who hangs around a host (without benefit to the host) in hope of gain or advantage

originFrom Middle English sponge, from Old English spunge, taken from Latin spongia, from Ancient Greek σπογγιά (spongiá), from σπόγγος (spóngos).

Etymology from Wiktionary, CC BY-SA 3.0