lawn tennis vs doubles

lawn tennis and doubles both are nouns.

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

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

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
doubles: tennis played with two players on each side

Other hyponyms of lawn tennis include professional tennis, singles, court tennis, real tennis, royal tennis.

lawn tennis (noun)	doubles (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	tennis played with two players on each side
	badminton played with two players on each side