| 单词 | keystones | 
| 释义 | keystonenoun  key·stone  ˈkē-ˌstōn  1   : the wedge-shaped piece at the crown of an arch that locks the other pieces in place   see arch illustration   2   : something on which associated things depend for support  determination, a keystone of the puritan ethic 3   or keystone species  : a species of plant or animal that produces a major impact (as by predation) on its ecosystem and is considered essential to maintaining optimum ecosystem function or structure   keystones nounas in cornerstonesan immaterial thing upon which something else rests a sense of history is the keystone to the city's draw as a tourist destination Synonyms & Similar Words Relevance 
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