MEETHAY, PERSIAN LIME VARIETY, CITRUS LATIFOLIA
In Urdu this fruit is called meethay, but this is a misnomer as meethay means sweet and this citrus fruit is far from being that. The nearest I could get to an English name for this is Persian Lime of which it might be a variant that is commonly grown in Pakistan and the rest of the subcontinent. It is ripe in monsoon season, which is now, and is used as a medicine or at least a health tonic, rather than for eating for pleasure.
It looks like an under-ripe orange as it has a thin green skin, and segments like an orange or other citrus fruit, but the juice is pale orange while the flesh might be yellow-orange tinged with green. The traditional medicine practitioners or hakims as they are called recommend that you have as much of this fruit as you can when it is in season so that you will be healthy for the rest of the year. It is good to detoxify the whole system, and is said to have a quinine-like effect so that if you eat this you are protected from malaria, just as you would be if you took quinine.

It also contains flavonoids with potent antioxidant properties which may inhibit the growth of cancerous cells in the body, by combating the free radicals which damage healthy cells.
It doesn’t seem to be the exact same thing as a Tahiti lime which is used as a synonym for a Persian lime in the US as this fruit has seeds. It is used in Ayurvedic medicine for all the above-mentioned ailments and also used to stimulate the secretion of gastric juices in the digestive tract, and to help if you have been exposed to the sun for too long. It also has antiseptic qualities.

It tastes rather like an especially tart grapefruit with lemon juice added, although this doesn’t quite describe the tart, astringent taste quite accurately. It isn’t used in cooking here to the best of my knowledge, although it might be a useful addition to a pickle, and if you have never tried one, then don’t get anxious about the fact!