The first Thai dictionary from 1873 CE (2416 in the Thai Buddhist calendar) defines kaeng as a watery dish to be eaten with rice and utilizing shrimp paste, onions or shallots, chillies, and garlic as essential ingredients. Coconut milk is not included in this definition and many Thai curries, such as kaeng som and kaeng pa, do not feature it. Curries in Lanna (northern Thai) cuisine, with only a few exceptions, do not use coconut milk due to coconut palms not growing well, if at all, in the climate of the Thai highlands. The spiciness of Thai curries depends on the amount and kind of chilli used in the making of the paste. Even within one type of curry the spiciness can differ widely.
