tennis racket vs racquet

tennis racket and racquet both are nouns.

Word	Noun	Adjective	Verb	Adverb
tennis racket	Yes	No	No	No
racquet	Yes	No	No	No

As nouns, racquet is a hypernym of tennis racket; that is, racquet is a word with a broader meaning than tennis racket:

tennis racket: a racket used to play tennis
racquet: a sports implement (usually consisting of a handle and an oval frame with a tightly interlaced network of strings) used to strike a ball (or shuttlecock) in various games

Other hypernyms of tennis racket include racket.

tennis racket (noun)	racquet (noun)
a racket used to play tennis	a sports implement (usually consisting of a handle and an oval frame with a tightly interlaced network of strings) used to strike a ball (or shuttlecock) in various games