In a way that is acceptable or tolerable, although not very good or very enjoyable.
Sufferably means something is okay, but not great. It's not bad, but it's not very good either.
Examples:
The food was sufferably good.
The movie was sufferably interesting.
She sang sufferably well.
The weather was sufferably warm.
The bed was sufferably comfortable.
He spoke sufferably loudly.