Colour and shape are the giveaway: a lemon is yellow and oval, a lime is green and round, with a sharper, more tart taste. If it is bright yellow on the outside, it is a lemon; if it is green and smaller, it is a lime.
The core difference
A lemon is a yellow, oval citrus fruit, while a lime is a smaller, round, green citrus fruit with a sharper flavour.
- Lemon — a yellow, oval citrus fruit with sour juice: Squeeze a lemon over the fish before serving.
- Lime — a small, round, green citrus fruit with a sharp, tart flavour: Squeeze a lime over the tacos.
How to tell them apart
Look and taste do most of the work: lemons are yellow, oval, and sour, while limes are green, rounder, and noticeably more tart. Both words stretch beyond the fruit itself. Lemon can describe a faulty or disappointing product, especially a car, as in a used car that turns out to be a total lemon, and it also works as an adjective for a pale yellow colour or lemon flavour.
Lime is the more crowded word of the two: besides the citrus fruit, it names a yellowish-green colour, the mineral calcium oxide or calcium hydroxide used in construction and farming, and even a completely unrelated tree, the linden, also called lime. Farmers, for instance, spread lime on acidic soil to raise its pH, which has nothing to do with the fruit at all.
