Use of the word "by" or "bye" as a no-game or off-week

Recently, looking at my softball schedule, noting several weeks in which our team has a "by," I wondered about the use and spelling of the word in this context. Of course you can't do a reasonable search of such a word, you get millions of hits! Mirriam-Webster doesn't seem to list this meaning, and I'm stumped. What is proper spelling and how do you suggest looking something like this up? Thanks in advance,

Dale Bix