Al ‧ i Ba ‧ ba /ˌæli ˈbɑːbɑː $ ˌɑː-/ BrE AmE
the main character in a story called Ali Baba and the Forty Thieves from The Arabian Nights . Ali Baba sees 40 thieves enter a secret ↑ cave (=a large hole in the side of a cliff or under the ground) by saying the magic words ‘Open Sesame’, which makes a door in the cliff open. He repeats these words, enters the cave, and takes some of the gold that the thieves keep there. When the thieves discover that Ali Baba knows their secret they decide to kill him. They hide in 40 large oil ↑ jar s (=round containers) which are delivered to his house, but Ali Baba’s servant hears about the trick and saves his master by pouring boiling oil into the containers and killing all the thieves.