The makrut lime leaf is the glossy, dark-green leaf of the makrut lime tree (Citrus hystrix) and one of the most fragrant leaves in all of cooking: torn or bruised, it releases an intense, almost shocking floral-citrus perfume, far brighter and more aromatic than the rind of any ordinary lime. It is the defining aroma of Thai, Lao, Cambodian, Malaysian and Indonesian kitchens — the green lift in tom yum and tom kha, in green and red curry pastes, in coconut curries, stir-fries and fish dishes — where it is used much like a bay leaf: dropped in whole to perfume a broth and fished out, or stacked, rolled and sliced into hair-fine threads (chiffonade) that are eaten. The knobbly fruit's zest is prized too, and the leaf is sometimes still sold under the older name 'kaffir lime', now widely retired because that word is a racial slur in several languages.