1. official permission or approval to do something
Usage: British spelling; American English uses 'authorization'; often used in formal or legal contexts
2. the act of giving someone the power or right to do something
Usage: often refers to granting authority or credentials

Examples

• You need written authorisation from the manager before making any major purchases.
• The bank requires authorisation for transactions over a certain amount.
• She received authorisation to lead the research project.
• The government granted authorisation for the new construction.
• Without proper authorisation, employees cannot access the secure files.
• The doctor's authorisation was necessary before the surgery could proceed.