Sentence:  Nor is it an accident that baseball , growing into the national game in the last 75 <WSD>years</WSD> , has become a microcosm of American life , that learned societies such as the American Folklore Society and the American Historical Association were founded in the 1880's , or that courses in American literature , American civilization , American anything have swept our school and college curricula . 
Meaning of the word marked with <WSD> tags:  a period of time containing 365 (or 366) days