There are several synonyms for the term "tennis bum." Some people might use the phrase "racket rat" to describe someone who spends most of their time on the tennis court. Others might call them a "tennis addict" or a "tennis fanatic." Some other terms that could be used to describe someone who spends a lot of time playing tennis might include "tennis enthusiast," "tennis fiend," or even "court junkie." Regardless of the terminology used, it's clear that those who love playing tennis often have a passion for the game that can be difficult to match.