A 莛 tíng or a 楹 yíng. Technically, this is "a blade of grass" or a "pillar." Here as elsewhere, Zhuangzi seems to be juxtaposing not only the differences between things but also the differences between words since they sound so similar, and thus by extension the difference between words and things. So it is important here that the words refer to things on opposite extremes of size, but also that the words themselves sound almost the same. Competing translations were "a blip or a blimp," "a mince or immense," and "a bunion or a Bunyon" (thanks to my friend, Tim Tyler, for that last one).