tennis vs court tennis

tennis and court tennis both are nouns.

Word	Noun	Adjective	Verb	Adverb
tennis	Yes	No	No	No
court tennis	Yes	No	No	No

As nouns, court tennis is a hyponym of tennis; that is, court tennis is a word with a more specific, narrower meaning than tennis:

tennis: a game played with rackets by two or four players who hit a ball back and forth over a net that divides the court
court tennis: an ancient form of tennis played in a four-walled court

Other hyponyms of tennis include professional tennis, singles, doubles, real tennis, royal tennis.

tennis (noun)	court tennis (noun)
a game played with rackets by two or four players who hit a ball back and forth over a net that divides the court	an ancient form of tennis played in a four-walled court