(to form a particular part of something): Teenagers account for the vast majority of our customers.
(explain the cause of something): How do you ac- for the sudden disappearance of the files?
(to be the cause of something): HIV accounted for over 20,000 deaths within two years.
(know the location of something): We have accounted for every item that was missing.
(to have record of how money has been spent): Your job as a treasurer is to ac- for every penny that we earned or spent.
(to think about something before): The authorities failed to ac- for the fact that the population is growing.