gandermooner – A husband who strays each month, during the "time of month" when his wife is "unavailable".
From the Dict. of Obsolete English: Gander, v. To ramble about without object. Gandermonth, s. The month in which a man's wife is confined. Gandermooner, one who acts the gallant at that season. To go a gandering, to gallant during this season.