The grammar gives structural relationships between categories. To parse a sentence we know to which categories the words in the sentence belong. This is the purpose of the lexicon. It assigns words to categories and gives them some attibute values and a semantic annotation.
Here is an example from the Squirrel lexicon:
department. n. [agreement,num] = sing. [agreement,pers] = 3. [gender] = neut. [vowel] = minus. [mass] = minus. [nlevel] = bare. [quest] = no. `department.