What does the cryptic crossword clue "A jam, when tennis player keeps bouncing the ball (8)" mean?

The wordplay uses a charade (building blocks). PRE (synonym="PRE") + SERVE (synonym="SERVE") = PRESERVE The answer is PRESERVE.

A jam, when tennis player keeps bouncing the ball (8)

Guardian Cryptic #29315 | 1 Down | 2024-02-26 flower