gratuity

gra|tu|ity /grətj'uːɪti, AM -t'uː-/ (gratuities)
1 [N-COUNT]
A gratuity is a gift of money to someone who has done something for you. (FORMAL)
The porter expects a gratuity.
= tip
2 [N-COUNT]
A gratuity is a large gift of money that is given to someone when they leave their job, especially when they leave the armed forces. (BRIT FORMAL)
He is taking a gratuity from the Navy.