Sentence:  Þa monðas þe habbað iiii <WSD>nonas</WSD> æfter kalendas... habbað to idus xiii dagas and to ii kalendas eahtatyne. / : Those months that have 4 <WSD>nones</WSD> after the kalends... have 13 days to the ides and eighteen to the second kalends. 
Meaning of the word marked with <WSD> tags:  The notional first-quarter day of a Roman month, occurring on the 7th day of the four original 31-day months (March, May, Quintilis or July, and October) and on the 5th day of all other months.