1. Concerning how something is just good enough: Jane mentioned, "This winter coat will passably do and keep me warm, I guess."

Many girls thought that Susan's brother was very handsome, but she thought he was just passably attractive.
2. Descriptive of how something is presented in a moderate or sufficient way or degree: Jack's mother thought that her son's high school grades were passably acceptable so as to apply to the junior college in town.