Sentence:  Let it not be lawful to use wicked observations of the <WSD>calends</WSD>, and to keep the gentiles' holy-days, nor to deck houses with bays or green boughs; for all this is an heathenish observation. 
Meaning of the word marked with <WSD> tags:  "Often with initial capital": the first day of a month, particularly  the first day of a month of the Roman calendar.