Second-class and Second class

Second-class adjective - Of little or less value or merit.

Second class and second-class are semantically related In some cases you can use "Second class" instead the phrase "Second-class" as a noun or an adjective.

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

Second-class and second class are semantically related in low topic. You can use "Second-class" instead the phrase "Second class" as an adjective or a noun or an adverb, if it concerns topics such as inferior, poor, mediocre, under.