I have issues with the following definitions:

Ballboy – A ballboy can only be male! The female counterpart is a ballgirl, and the generic term is ballperson.

Counterpuncher – A counterpuncher is not necessarily defensive. She absorbs the pace of her opponent and uses it against her, rather than generating her own pace.

Lawn-tennis – Can also be played on clay, carpet or hard courts. It’s the term that distinguishes the tennis we know from the ancient game called real tennis.

Let – For a ‘let’ serve, only the serve is replayed, not the whole point. However, if a let occurs after the serve (e.g. a foreign object appears on the court), then the whole point is replayed and you get a first serve.

Unforced error – The definition should be reworded to avoid implying that unforced errors can only occur on the serve or return of serve (the word “return” should be reserved exclusively for returns of serve).

And I would like to suggest adding the following terms:

Ad-court
(hit back) Behind
Body-jamming serve
Bye
Carpet
Centre-line
Challenge
Changeover
Chip and charge
Choke
Clay
Coach
Code-violation
Continental grip
Cyclops
Default
Draw
Drive
Drive-volley
(taking the ball) Early
Floater
Forced error
Foot-fault
Game
Golden set
Grass
Groundstaff
Gut-saver
Half-volley
Hard court
Hawkeye
Heavy ball
I-Formation
Initiative (in a rally)
Intercept
ITF
Knockout-draw
Long
Lucky Loser
Medical Time-Out
Momentum
Moonball
Net
Netcord
Off-forehand/backhand
One-two punch
Order of play
Overhead
Punch-volley
Qualifier
Race
Ranking
Rebreak
Retire
Retriever
Return
Round robin
Seed
Set
Sideline
Sidespin
Selesian (two hands both sides)
Semi-Western grip
Serve down the middle
Serve out wide
Service-box
Service-line
Split step
Spread
Stop-volley
Tempo
Throw (a match)
Touch
Trainer
Unseeded
Volley
Warm-up
Western grip
Wide
Wrong-foot

Thanks! I checked out your site and added it to my RSS reader. You are definitely off to a good start!