1. second侧重顺序，意思是“第二”，与“第一”“第三”等相对比而言。如：
Argentina is the second biggest nation in Latin America. 阿根廷是拉丁美洲第二大国。
Several candidates were called for a second interview. 有几个候选人被叫来作第二次面试。
His second suggestion was little better than his first. 他的第二个建议比第一个好不了多少。
2. secondary侧重重要性或价值，意思是“第二位的”“次要的”。如：
Other people’s opinions are secondary—it’s my opinion that counts. 其他人的意见是次要的，我的意见才重要。
What matters is the size of the office. The location is of secondary importance. 关键是要看办公室的大小，位置是次要的。