Forgivable things can be condoned, excused, or understood. If you have 30 cousins, it's completely forgivable for you to forget whose birthday falls on which day.
If your favorite teacher is funny, fair, and smart, you'll find her tendency to use terrible puns totally forgivable. And on a slick, snowy road, another driver will probably consider the gentle slide of your car into her car's bumper utterly forgivable. Forgivable comes from the verb forgive, which has an Old English root, forgiefan, "give, allow, or pardon."