4 definitions
Definition.com
Doing someone a favor (n.) is generosity with a memory.
Definition.com
Doing someone a favor (n.) creates a debt neither party wants to name.
Definition.com
Doing someone a favor (n.) is a gift that comes with a receipt, quietly kept by both parties
Definition.com
Doing someone a favor (n.) is remembered in detail by the one who did it and vaguely by the one it was done for