vocabulary / dictionary
vocabolari
voh-kah-boh-LAH-ryoh
Has two meanings: the vocabulary (words you know) and the dictionary (reference book). Context makes it clear.
Usa il vocabolario se non capisci una parola.
Use the dictionary if you don't understand a word.
Ho imparato molto vocabolario nuovo questa settimana.
I learnt a lot of new vocabulary this week.