Sentence:  However , if their United States income is not subject to the withholding of tax on wages , their returns are due June 15 , 1962 , if they use a calendar year , or the 15 th day of the 6 th <WSD>month</WSD> after the close of their fiscal year . 
Meaning of the word marked with <WSD> tags:  one of the twelve divisions of the calendar year