The Collaborative International Dictionary
off-day
off-day \off-day\ n. A day when things go poorly; as, I guess this is one of my off-days.
WordNet
off-day
n. a day when things go poorly; "I guess this is one of my off-days"
Usage examples of "off-day".
It's only that I'm thinking of taking my family in that direction in the Long, and it occurred to me that, as very few of the English preceptories have ever been properly planned, I might have an opportunity of doing something useful on off-days.