Lemons were a citrus fruit on Earth, they were related to oranges.
The planet Oroobia had the general scent of lemons when the Doctor and Donna Noble visited. (NSA: The Doctor Trap)
In drinks
Whilst in 1936 Donna Noble consumed a "sidecar" (Cognac, orange liqueur and lemon juice). (DW: The Unicorn and the Wasp)
The Doctor preferred lime to lemon in his Bombay Sapphire Gin when he drank with Iris Wildthyme. (PDA: Verdigris)
