 Definitions sought by philosophers are not of the sort found in a dictionary. Frege’s definition of number (1884) and Alfred Tarski’s definition of truth (1983, ch. 8) are not offered as candidates for dictionary entries. When an epistemologist seeks a definition of “knowledge,” she is not seeking a good dictionary entry for the word ‘know’. The philosophical quest for definition can sometimes fruitfully be characterized as a search for an explanation of meaning. But the sense of ‘explanation of meaning’ here is very different from the sense in which a dictionary explains the meaning of a word.