second-class 1 adj. 1. Belonging in the class that is next to the highest or next best. He was only a second-class math student. His parents traveled as second-class passengers on the boat. The periodical came as second-class mail.
Compare: FIRST-CLASS, THIRD-CLASS. 2. Not so good as others; second-rate. They were never given full democratic rights but were always treated as second-class citizens.
second-class 2 adv. By second class. We went second-class on the train to New York. I mailed the newspaper second-class.