Second class and Second-string

Second class noun - Not the highest quality in a classification.

Second-string and second class are semantically related. in under topic. In some cases you can use "Second-string" instead an adjective phrase "Second class".

Second-string adjective - Being a replacement or substitute for a regular member of a team.

Second class and second-string are semantically related. Sometimes you can use "Second class" instead an adjective phrase "Second-string".