tennis vs lawn tennis

tennis and lawn tennis both are nouns.

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

As nouns, tennis and lawn tennis are synonyms defined as:

tennis and lawn 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

tennis (noun)	lawn 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	a game played with rackets by two or four players who hit a ball back and forth over a net that divides the court