Eggplant and Mad apple

Eggplant noun - Egg-shaped vegetable having a shiny skin typically dark purple but occasionally white or yellow.

Mad apple is a synonym for eggplant. In some cases you can use "Mad apple" instead a noun "Eggplant".

Mad apple noun - Hairy upright herb native to southeastern Asia but widely cultivated for its large glossy edible fruit commonly used as a vegetable.

Eggplant is a synonym for mad apple. You can use "Eggplant" instead a noun phrase "Mad apple".