gratuity

As nouns the difference between gratuity and autograt

is that gratuity is a reward, service, or payment provided freely, without obligation while autograt is (informal|rare|neologism) a gratuity automatically added to a bill.

As nouns the difference between gratuity and donative

is that gratuity is a reward, service, or payment provided freely, without obligation while donative is a gift; a largess; a gratuity.

As an adjective donative is

of, pertaining to, or being a donation.

As nouns the difference between gratuity and tippee

is that gratuity is a reward, service, or payment provided freely, without obligation while tippee is the recipient of a gratuity.